. A textbook of botany for colleges and universities ... Botany. 932 ECOLOGY incapable of germination for several years. There are some plants (as the cocklebur, red clover, and black locust) in which some of the seeds appear ordinarily to require a longer time than do others before they are capable of germination. It is probable that in most of these cases delay in germination is due to the impermeabihty of the testa (see below). Yet it is conceivable that in seeds, as in buds, various maturing processes take place after the attainment of apparent maturity; detach- ment from the carpel and ap
. A textbook of botany for colleges and universities ... Botany. 932 ECOLOGY incapable of germination for several years. There are some plants (as the cocklebur, red clover, and black locust) in which some of the seeds appear ordinarily to require a longer time than do others before they are capable of germination. It is probable that in most of these cases delay in germination is due to the impermeabihty of the testa (see below). Yet it is conceivable that in seeds, as in buds, various maturing processes take place after the attainment of apparent maturity; detach- ment from the carpel and apparent rest may not mean the cessation of maturing activities. Possibly the delayed germination of the hawthorn {Crataegus) is to be thus explained, since the removal of the testa and exposure to good germination conditions seems for a certain period in- effective.' The most remarkable of all cases of delayed germination is afforded by the spores of Lycopodium, which seem to require a rest of three to fifteen years before they are able to develop. The relation of the testa to delayed germination. ââ The common cocklebur {Xanthium canadense) has two seeds in each fruit, differing somewhat in shape and in position (fig. 1228), and it has been found that the seed nearest the base usually germi- nates the first spring after maturation, while the upper seed commonly does not germinate until the second spring. In many species some seeds germinate long before others, and it is not unlikely that in some cases the seeds of a given crop may germinate over a period of three or more years. Such a condition seems advantageous, especially in annuals, since it insures the persistence of a species, even though certain seasons prove unfavorable for seed development. In Xanthium, it has been shown that the delayed germination of the upper seed is due to the fact that its testa is less permeable to oxygen than is that of the lower seed. In nature the lower seed is exposed first to good germinat
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectbotany, bookyear1910
