CHAPTER VI GERMINATION 



Seed characters that facilitate or retard germination. Introductory 

 statement. Probably most seeds are able to germinate at maturity, if 

 suitable conditions are present. However, there are many seeds which, 

 under ordinary natural conditions, require the lapse of a longer or 

 shorter period before germination is possible. Such delayed germina- 

 tion may be due to a lack of actual maturity in spite of appearances, 

 or, more commonly, to enveloping structures that retard the germinative 

 processes. There are some seeds which ge minate in natural condi- 

 tions the moment that maturity is reached, the best illustration of such 

 a habit being afforded by viviparous plants. 



Vivipary. Viviparous plants are those in which the embryo con- 

 tinues in a state of uninterrupted development from the outset. Since 

 a period of rest between two periods of sporophyte activity is the chief 

 distinguishing feature of the seed, it is obvious that viviparous plants are 

 essentially seedless, and hence do not in the usual sense exhibit germina- 

 ation. The best examples of vivipary are the mangroves (especially 

 Rhizophora and Bruguiera). In the American mangrove (Rhizophora 

 Mangle) the " seedlings " develop a large, green, pointed structure, 

 mainly a greatly enlarged hypocotyl, which protrudes from the fruit (figs. 

 1225, 1226), and which finally becomes so heavy that the "seedling" 

 drops into the mud beneath; since this structure is heaviest toward the 

 lower end and is much more massive than the plumule, the " seedling " 

 falls right side up into the mud and continues growing, soon striking root 

 and exhibiting vigorous plumule development (fig. 1227). Vivipary has 

 been regarded as advantageous to the mangroves, since ordinary seeds 

 might not be able to germinate in the oozy slime beneath the trees. 

 Currents frequently bear the fallen " seedlings " to neighboring shores, 

 so that the viviparous habit also facilitates dispersal; as the young 

 plants float in an erect position, they readily lodge in places which 

 are suitable for further growth. 



Some alpine plants exhibit vivipary, notably species of Poa and Polygonum, 

 but the advantage, if any, is not evident. Somewhat comparable to vivipary is the 



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