Project Director

Edwards, Maurice E.


Dept. of Biological and Environmental Sciences


University of Tennessee at Chattanooga

Place of Publication

Chattanooga (Tenn.)


As plants evolve into new forms and shapes, the reproductive structures are often the last to change because of the importance of successful reproductive organs to the survival of the plant's hereditary information. Because of this particular feature, one very common method of determining how advanced a species is evolutionarily is the study of its reproductive cycle (Gifford and Foster, 1989). A few advanced classes, most notably the general class groupings of the Gymnosperms and Angiosperms, have developed seeds as a part of their reproductive cycle. Normally, there are several stages through which the seed must go in order for it to germinate properly and survive: fertilization, maturation (ripening), dispersal, dormancy, after-ripening, germination, and finally seedling establishment (Fenner, 1985). At the end of each of these stages, there is a reduced number of survivors in the seed population. For instance, the coastal redwood tree produces between one and ten billion seeds in its lifetime, yet merely a single seed is required to replace the parent. Obviously there will not normally be a one hundred percent survival rate among these seeds; most of them die. Although it may seem wasteful, this graduated process selects against the least fit seeds, insuring that only the fittest survive to germination, which in tum allows the species as a whole to survive and thrive. Due to their reproductive strategy, weeds often have interesting and varied reproductive patterns. Of particular importance to this discussion, however, is the after-ripening stage The term after-ripening is often used to refer to the process. often occurring during the dormancy period, that prepares the seed for germination. This area of developmental biology is understudied, and consequently the process is not very well understood. The after-ripening process has never been ascribed to any single event, and is usually considered to be the result of multiple factors (Mayer and Poljakoff-Mayber, 1988). Many things influence the seed's ability to germinate and can be considered to influence the after-ripening process. For instance, seed drying, embryo nutrient depletion, seed coat weakening or cracking, chemical inhibitor leaching or chemical germination promoters have all been implicated as major factors in both dormancy-breaking and/or after-ripening. The factors influencing the after-ripening process in pokeweed seeds are not very well understood and as a major process in seed development and the germination process, it deserves better comprehension. Through my research, I plan to provide greater knowledge of this aspect of the germination process. In particular, I will research the seed coat's (also known as the testa) role in the afterripening of pokeweed (Phytolacca americana). Several factors of the seed coat could play a prominent part in this role, among these are the mechanical strength of the testa which could possibly restrain the growth of the embryo until this obstacle has been removed or weakened: the possible water-impermeability of the seed coat, preventing the embryo from imbibing the water which is necessary for germination; the impermeability of the testa to the leaching-out of germination inhibiting chemicals within the embryo. These are merely a few of the possibilities, and it is likely that there are other aspects of the seed coat which influence dormancy as well. Through the course of my experiments I plan to illuminate the particular aspect of the seed coat which has the greatest influence on the after-ripening process.


B. S.; An honors thesis submitted to the faculty of the University of Tennessee at Chattanooga in partial fulfillment of the requirements of the degree of Bachelor of Science.




Pokeweed--Reproduction; Pokeweed--Seeds--Production (Biology); Germination; Seeds--Dispersal


Plant Biology

Document Type



ii, 51 leaves





Call Number

LB2369.5 .C69 1993


Included in

Plant Biology Commons