The phylogeny of the stamen
About: This article is published in American Journal of Botany.The article was published on 1937-12-01. It has received 65 citations till now. The article focuses on the topics: Stamen.
Citations
More filters
TL;DR: The evidence concerning the modification of sex expression in the sporophytes of flowering plants by external agencies, excluding those which act through genetical paths, is summarized.
Abstract: SUMMARY
1. This article summarizes the evidence concerning the modification of sex expression in the sporophytes of flowering plants by external agencies, excluding those which act through genetical paths.
2. Three of the primary variables of the plant environment, mineral nutrition, light regime and temperature regime, directly influence sex expression in hermaphrodite, monoecious and dioecious species; their effects, moreover, are reasonably consistent. In general:
(a) High levels of nitrogenous nutrition promote femaleness and depress maleness.
(b) In short-day plants and some day-neutral plants whose development is accelerated by short days, short-day treatment promotes female and depresses male sex expression. Low levels of light intensity during growth may also inhibit staminal development. In one long-day plant, spinach, it seems probable that short days lead to the production of male flowers on plants which in normal photoperiod would be phenotypically female.
(c) Low temperatures, particularly when experienced through the dark period of a daily photoperiodic cycle, promote female sex expression and depress male.
3. Sporophyte sex expression may be modified through certain chemical agencies. In one experiment with Melandrium dioicum, the animal sex hormones have been shown to affect sexuality, oestrone, oestradiol and oestradiolbenzoate promoting the development of pistillate structures in the flower, and testosterone and testosterone propionate of staminate.
In monoecious cucurbits, applied auxins simultaneously suppress early flowering, accelerate the appearance of female flowers and increase their over-all proportion; a-naphthaleneacetic acid is the most effective auxin in this role. Similar effects are produced in cucumber by exposure to atmospheres containing low percentages of carbon monoxide.
Under some circumstances, the general growth-suppressor maleic hydrazide may differentially inhibit micro- and megasporogenesis in hermaphrodite and monoecious species, so altering the functional sex balance.
4. Certain forms of mutilation affect sex expression. The reduction of leaf surface and of volume of storage tissue militates against female sex expression in one genus of monoecious aroids. The removal of fruits and female flowers in certain monoecious genera increases the over-all proportion of female flowers formed. Severe mutilation involving the regeneration of new leading shoots during recovery may lead to later anomalies in sex expression in a number of monoecious and dioecious species.
5. In grafting experiments with dioecious species, no authentic cases of the influence of a stock of one sex upon the sexuality of a scion genetically of the other have been recorded.
6. The interrelationships of the hypothetical flowering hormone (florigen), auxin and plant sexuality are discussed. In general, photoperiodic treatment which causes early and heavy flowering also promotes female sex expression as against male; also, factors which raise the auxin levels available at the differentiating apex promote femaleness and suppress maleness. These facts appear paradoxical, since, at least in short-day plants, high auxin levels inhibit the transition from the vegetative to the flowering state. It seems probable, however, that while low auxin levels may be necessary for the initiation of flowering, auxin is necessary for flower development after the formation of the primordia. It may be that in those plants which are accelerated throughout the entire course of flowering by short-day treatment, such treatment actually increases auxin availability at the apex after the first period of flower initiation.
7. A rationalization of two apparently contradictory responses along these lines would permit the formulation of an hypothesis that floral organogenesis is regulated, although not determined, by auxin levels at the apex. Much of the existing evidence would be explained by the assumption that the growth of stamen and pistil primordia is governed by auxin in the characteristic manner, the response following an optimum curve. It seems that the concentration causing maximal stamen growth is lower than that promoting maximal pistil growth, so that auxin level at the differentiating apex determines the sex balance of the flowers produced. In some plants it is probable that this level is susceptible to control in the apex by influences such as temperature, and through the auxin economy of the whole plant, by such factors as nutrition and photoperiodism. It is through these agencies that the sex balance of the flowers may be modified.
252 citations
245 citations
TL;DR: The present paper focuses on the development of plant classification in the Linnaean and Pre-Darwinian systems and describes the various systems that emerged during this period.
Abstract: INTRODUCTION Scope of the Paper 247 Derivations and Definitions of Terms .248 HISTORICAL DEVELOPMENT OF PLANT CLASSIFICATION . .252 Pre-Linnaean Systems 252 Linnaeus 256 Post-Linnaean and Pre-Darwinian Systems .256 Darwin .264 Post-Darwinian Systems 266
131 citations
TL;DR: This work advocates maintenance of parallel, reciprocally illuminating programmes of morphological and molecular phylogeny reconstruction, respectively supported by homology testing through additional taxa and evolutionary-developmental genetic studies that explore genes potentially responsible for major phenotypic transitions.
Abstract: Recent attempts to address the long-debated 'origin' of the angiosperms depend on a phylogenetic framework derived from a matrix of taxa versus characters; most assume that empirical rigour is proportional to the size of the matrix. Sequence-based genotypic approaches increase the number of characters (nucleotides and indels) in the matrix but are confined to the highly restricted spectrum of extant species, whereas morphology-based approaches increase the number of phylogenetically informative taxa (including fossils) at the expense of accessing only a restricted spectrum of phenotypic characters. The two approaches are currently delivering strongly contrasting hypotheses of relationship. Most molecular studies indicate that all extant gymnosperms form a natural group, suggesting surprisingly early divergence of the lineage that led to angiosperms, whereas morphology-only phylogenies indicate that a succession of (mostly extinct) gymnosperms preceded a later angiosperm origin. Causes of this conflict include: (i) the vast phenotypic and genotypic lacuna, largely reflecting pre-Cenozoic extinctions, that separates early-divergent living angiosperms from their closest relatives among the living gymnosperms; (ii) profound uncertainty regarding which (a) extant and (b) extinct angiosperms are most closely related to gymnosperms; and (iii) profound uncertainty regarding which (a) extant and (b) extinct gymnosperms are most closely related to angiosperms, and thus best serve as 'outgroups' dictating the perceived evolutionary polarity of character transitions among the early-divergent angiosperms. These factors still permit a remarkable range of contrasting, yet credible, hypotheses regarding the order of acquisition of the many phenotypic characters, reproductive and vegetative, that distinguish 'classic' angiospermy from 'classic' gymnospermy. The flower remains ill-defined and its mode (or modes) of origin remains hotly disputed; some definitions and hypotheses of evolutionary relationships preclude a role for the flower in delimiting the angiosperms. We advocate maintenance of parallel, reciprocally illuminating programmes of morphological and molecular phylogeny reconstruction, respectively supported by homology testing through additional taxa (especially fossils) and evolutionary-developmental genetic studies that explore genes potentially responsible for major phenotypic transitions.
122 citations
Cites background from "The phylogeny of the stamen"
...As noted by adherents of Zimmerman’s telome theory (Zimmerman, 1930, 1938), such as Wilson (1937), spore-bearing organs (i.e. sporangia) evolved before leaves in early land plants....
[...]
References
More filters
177 citations
TL;DR: Goethe's theory of the equivalence of the vegetative shoot to the flower, in the angiosperms, is discussed and an attempt is made to evaluate the evidence for it.
Abstract: Summary
In the introduction to this study, the chief phases in the interpretation of the flower, from Goethe's day onwards, are briefly indicated in their historical sequence. Goethe's theory of the equivalence of the vegetative shoot to the flower, in the angiosperms, is then discussed and an attempt is made to evaluate the evidence for it. It is shown that this theory, if understood in a broad sense, harmonizes with the modern holistic trend in morphology. It is suggested that the flower is comparable with a vegetative shoot in a condition of permanent infantilism. Special emphasis is laid upon the inflorescence as offering, in some respects, an intermediate term between the vegetative shoot and the flower.
After a brief consideration of bracts, sepals, petals and stamens, the Candollean theory of the carpel is discussed, and it is concluded that it has been peculiarly successful in providing a framework for the vast plexus of facts which it is its task to correlate. Some of the difficulties which have been felt in regard to this theory are considered, with special reference to recent work on the gynaeceum structure of the Papaveroideae. The stigma and “transmitting tissue” are then discussed, and it is concluded that there is nothing in the behaviour of this tissue which is out of harmony with the Candollean theory of the carpel.
An attempt is made to arrive at a more precise notion of the meaning to be attached to correspondence, equivalence and homology, when these terms are used in connexion with Goethe's comparison of the vegetative and reproductive parts. It is suggested that these terms are best translated into the language of modern thought by the word parallelism, thus avoiding the use of Goethe's type concept, which cannot be safely employed unless its abstractness is constantly borne in mind.
The nineteenth-century phase, in which morphological ideas were lifted bodily into an historical setting, is then discussed, and emphasis is laid upon the danger of thus confusing two irreducible worlds of thought. Certain attempts which have been made to relate the flower of the angiosperm to the reproductive organs of plants of earlier geological periods are briefly criticized.
In the concluding sections, attention is drawn to the current reaction against phylogenetic morphology, and in favour of the purely comparative morphology contemplated by Goethe. A slight sketch is given of Delpino and Troll's theories of the flower, in which “form” is considered as distinct from “organization”. Whether these views are accepted or not, the “Gestaltlehre” is at least an indication that the morphological ideas, which Goethe initiated before the end of the eighteenth century, may even to-day suggest fresh approaches to the problem of the interpretation of the flower.
74 citations
53 citations
TL;DR: The "classical theory" (as it is often termed in current literature) of the origin of the carpel is that it was derived from an infolded foliage leaf, which is generally accepted.
Abstract: EVJER SINCE the appearance of Goethe's essay on the " Metamorphosis of Plants " in 1790, the nature of the carpel has been a leading subject of discussion among botanists. Linked as it is with the question of the origin of the angiosperms, an understanding of the carpel is needed in the construction of a natural system of plant classification. The carpel was at first studied in its external form (the method of organography), but following the classical work of Van Tieghem ( 1875), investigation has centered on its vascular anatomy. It has been found that ancestral conditions of structure, long since lost to external view, may often be represented by a lingering vascular supply. Plant vascular tissue, like the skeleton of animals, is slow to change. Only the fossil remains themselves can show more, and well authenticated proto-angiosperm fossils are yet to be found. In previous anatomical studies of the carpel, comparatively little consideration has been given to the style and stigma. Excepting the conclusions of Brown (1866), the studies of style and stigma bore little morphological import until recent years. The subject was re-opened when Saunders (1925-1934, 19281931) urged a new explanation for the commissural stigmas described by Brown. This was in connection with the theory of carpel polymorphism. Although that theory in itself has only clouded the issue (Eames, 1931), at least the attention thereby called to the stigma has served to suggest this new line of attack upon the problem of the carpel. DIsCITSSION.The "classical theory" (as it is often termed in current literature) of the origin of the carpel is that it was derived from an infolded foliage leaf (fig. 1) 2 This explanation is generally
33 citations
TL;DR: Eichler as discussed by the authors argued that a typical shoot consists of the leaves and the axis, which are not really to be regarded as different organs, but fundamentally as parts only of one organ, and that the leaves are fundamentally nothing more than processes, or outgrowths of the axis of the shoot.
Abstract: The origin of the tendency among the earlier morphologists to draw a sharp distinction between stem and leaf may most probably be traced to the fact that vegetable morphology was first pursued as a science in regions where deciduous trees prevail. Seeing the leaves of so many plants fall off as a whole, while the scar left was almost a direct continuation of the external surface of the stem, doubtless gave rise to the view that the two should be regarded as radically distinct members. As the science of morphology progressed it became necessary, if this distinction were to be maintained, to define more clearly how members belonging to these two categories differ one from another. Various attempts were made by authors to show in what the essential difference consisted, the most notable being that of Hofmeister, who brought forward a number of distinctions, based chiefly upon development. The most essential of these were adopted in that section of the Text Book of Sachs, which deals with the relations of leaves and leaf-forming axes. In the last paragraph (No. 8) of that section, he clearly lays down the principle that “the expressions stem and leaf denote only certain relationships of the parts of a whole— the shoot.” This principle is elaborated in his more recent lectures, in which he writes as follows:— “A typical shoot consists of the leaves and the axis, which however are not really to be regarded as different organs, but fundamentally as parts only of one organ . . . . . In their nature, and as shown by the history of their development, the leaves are fundamentally nothing more than processes, or outgrowths of the axis of the shoot. . . . . ” If we accept these propositions, and I do not see how we can do otherwise, the same method of morphological treatment should be applied to the leaf as is usual in studying the stem. On reading current morphological papers, however, it is very apparent that this is not done. Leaving out of account the use of that adhesive terminology, which constantly revives in the mind the older mode of viewing the leaf, it is still obvious that the treatment of the leaf by modern writers is different from that of the stem. Thus, to take as an example the best of the earlier works on leaf-development, viz., Eichler’s Dissertation on the Development of the Leaf; after defining the Primordial Leaf as the young leaf before internal differentiation, or distinction of external parts, the author goes on to describe (p. 7) how the primordial leaf becomes differentiated into “ two chief parts, which are common to the leaves of all Phanerogams, viz., a stationary zone, which takes no part in the further formation of the leaf, and a vegetative part which forms the lamina with its branches.” The former he names the foliar base (blattgrund), and the products of its development are the sheath and the stipules if present; the latter he designates the upper leaf (oberblatt), which gives rise to the simple or branched lamina. The petiole is also, according to Eichler (p. 8), derived from the upper leaf, though other more recent writers describe it as being intercalated between the two parts. This distinction first drawn by Eichler has recently been revived, and the terminology, with some slight modifications, adopted by Goebel. He has however imposed a very necessary limitation upon its application, viz.: that the two parts of the primordial leaf “are not sharply marked off from one another, but are only to be distinguished by the part which they play in the further growth of the young leaf. ” He has, on the other hand, extended it to the Monocotyledons and Gymnosperms, and occasionally also to certain Cryptogams, in which similar phenomena appear. Thus the distinction of the foliar base and upper leaf has become established in botanical terminology, and it is applied equally to both branched and unbranched leaves.
32 citations