How to Do Things With Words

Mind, Self and Society from the Standpoint of a Social Behaviorist

What determines the number and size of the seeds produced by a plant? How often should it reproduce them? How often should a plant produce them? Why and how are seeds dispersed, and what are the implications for the diversity and composition of vegetation? These are just some of the questions tackled in this wide-ranging review of the role of seeds in the ecology of plants. The authors bring together information on the ecological aspects of seed biology, starting with a consideration of reproductive strategies in seed plants and progressing through the life cycle, covering seed maturation, dispersal, storage in the soil, dormancy, germination, seedling establishment, and regeneration in the field. The text encompasses a wide range of concepts of general relevance to plant ecology, reflecting the central role that the study of seed ecology has played in elucidating many fundamental aspects of plant community function.

The ecology of seeds

THE human brain is the instrument of the high powers of intelligence that distinguish man from all other living creatures. The secret of man's most distinctive attribute is hidden in the texture of his brain, and perhaps will never be fully revealed. Yet from time to time, with the growth of knowledge and the discovery of new methods of approach, we can profitably return to this greatest of all biological problems and get new glimpses of the factors that have made man what he is. Two considerations make the present time appropriate for taking stock of the state of our knowledge of these matters. The emergence of a clearer understanding of the sequence of structural changes in the brain and body of man's ancestors enables us to interpret the physiological factors involved in the widening and deepening of the intellectual powers and to appreciate the conditions essential for the attainment of-such mental growth. In the second place, the new points of view regarding the functions of the cerebral cortex that have emerged from Dr. Henry Head's suggestive clinical investigations prompt one to examine the brain anew and endeavour to integrate the results of his brilliant analysis with those revealed in the study of the evolution of the brain. Whether or not it is yet possible fully to correlate the facts and conclusions of these two disciplines into one coherent body of doctrine, it is well worth while to make the attempt to do so, if for no other reason than to direct attention to new problems that call for solution.

The Human Brain

Woltering, E. J. and Van Doom, W. G. 1988. Role of ethylene in senescence of petals—morphological and taxonomical relationships.—J. exp. Bot. 39: 1605-1616. Petal senescence in mature flowers was studied in 93 species from 22 families. The initial symptom of senescence was either wilting or abscission, but in some species the time span between wilting and abscission was very short. There was no apparent relationship between corolla form (choripetalous or sympetalous), ovary position (inferior or superior with respect to the corolla) and type of senescence (initial wilting or initial abscission). In monocots no initial abscission was found, while in dicots the difference between the wilting type and the abscission type was generally at the family level. With respect to petal senescence, sensitivity to exogenous ethylene (C2H4) was also related to the family level. Except for a few families (all tested Campanulaceae, Caryophyllaceae and Malvaceae, and most Orchidaceae), most of the flowers investigated that showed initial wilting were not sensitive to exogenous ethylene, e.g. all tested Compositae, Iridaceae, and Liliaceae. Most of the flowers showing initial abscission were sensitive to exogenous ethylene (Geraniaceae, Labiatae, Ranunculaceae, Rosaceae, Scrophulariaceae). Experiments with silver thiosulphate (STS) confirmed the effects of exogenous ethylene, both in flowers showing initial wilting and in flowers showing initial abscission. The data indicate, therefore, that ethylene is involved in the natural senescence of only a minority of the wilting type of flowers and in a majority (if not all) of the abscising type of flowers. Key words—Abscission, ethylene, senescence, silver thiosulphate.

Role of Ethylene in Senescence of Petals—Morphological and Taxonomical Relationships

Normal senescence of Petunia hybrida L. (cv. Pink Cascade) was associated with a 10-fold increase in their ethylene production. Soon after pollination wounding of the stigma of detached flowers there was a burst of ethylene production by the gynoecium, which reached a maximum after 3 h. A subsequnt more gradual rise in ethylene production by the flowers was accompanied by blueing, wilting, and senescence of the corolla. Treatment with 1 μl ethylene 1−1 accelerated the onset of senescence as measured first by color change and then by wilting of the corolla. These changes were further accelerated by using older flowers or higher concentrations of ethylene. Senescence was also hastened by supplying 1-aminocyclopropane-1-carboxylic acid (ACC) through the flower pedicel. Petunia pollen contained high concentrations of ACC (300 nmol g−1); treatment of stigmas with ACC (1 mM) caused a 4-fold increase in their ethylene production. Senescence, whether natural or hastened by pollination or piercing, was delayed by treating the flowers with the anionic silver thiosulfate complex.

Roles of ethylene and 1‐aminocyclopropane‐1‐carboxylic acid in pollination and wound‐induced senescence of Petunia hybrida flowers

Ethylene production and senescence of petals of pollinated carnation flowers were not prevented by removal of the ethylene produced by the gynoecium, suggesting that these events are a response to movement from the gynoecium of some stimulus other than ethylene gas. Application of 1-aminocyclopropane-1-carboxylic acid (ACC) to the stigmas caused an initial increase in gynoecium and petal ethylene production similar to that reported for pollinated flowers. This response was not seen in flowers whose stigmas were treated with indoleacetic acid (IAA). When [2-14C]ACC was applied to the stigmas of carnation flowers, radioactive ethylene was produced both by the gynoecia and by the petals. The possibility that ACC, transported from the stigmas to the petals, is responsible for the postpollination changes in carnation flowers is discussed.

http://ucce.ucdavis.edu/files/datastore/234-881.pdf

1-aminocyclopropane-l-carboxylic acid (ACC)—The transmitted stimulus in pollinated flowers?

Very low ethylene production rates were measured in nonpollinated Cyclamen persicum Mill flowers, and no change in production was observed during the whole life span of the flower until death. Normal senescence was accompanied by a gradual discoloration and loss of turgor followed by wilting. Pollination induced a dramatic increase in ethylene evolution, culminating in a peak 4 days after pollination, and abscission of the corolla on that day. Silver-thiosulfate, an inhibitor of ethylene action, had no effect on longevity of unpollinated flowers, but completely nullified the effect of pollination on corolla abscission. Exposing unpollinated flowers to very high ethylene concentrations (50 microliters per liter) for 48 hours did not promote corolla abscission or senescence. 1-Aminocyclopropane-1-carboxylic acid, the immediate precursor of ethylene, increased ethylene production by unpollinated flowers more than 100-fold, but did not promote corolla abscission. 1-Aminocyclopropane-1-carboxylic acid did enhance corolla abscission of pollinated flowers. It is concluded that the main effect of pollination in inducing corolla abscission of cyclamen is by rendering the tissue sensitive to ethylene, apart from the promotion of ethylene production.

http://www.plantphysiol.org/content/plantphysiol/75/4/1090.full.pdf

Does Pollination Induce Corolla Abscission of Cyclamen Flowers by Promoting Ethylene Production

http://ucce.ucdavis.edu/files/datastore/234-870.pdf

C.S. Whitehead

Papers

Roles of ethylene and 1‐aminocyclopropane‐1‐carboxylic acid in pollination and wound‐induced senescence of Petunia hybrida flowers

1-aminocyclopropane-l-carboxylic acid (ACC)—The transmitted stimulus in pollinated flowers?

Does Pollination Induce Corolla Abscission of Cyclamen Flowers by Promoting Ethylene Production

Identification of the ethylene precursor, 1-aminocyclopropane-1-carboxylic acid (ACC), in pollen

Role of ethylene and short-chain saturated fatty acids in the smoke-stimulated germination of Cyclopia seed