99 



N 



bered that in some cases it is of great importance to the 

 young plant that the plumule should be kept free from the 

 surrounding plants, so as to be more exposed to the air and 

 light. And we have seen, for instance, in the germinating 

 plantlets oi B^ammculiis abortivtis, R. reciirvatus, Sjirraceiiia, 

 Saxifraga and Saniatla, how the hypocotyl gradually is 

 forced to bend down to the ground, after the first leaves have 

 developed. The plant attains the same protection as Ipomcva 

 and Djlphmhun, only at a later stage, and it is well attached 

 to the ground by the development o^ roots from, the upper 

 part of the hypocotyl in connection with the more or less 

 persistent primary root and the earlier developed secondary 

 ones. It is to be supposed that this manner of germinating, 

 with the rooting hypocotyl and the primary root dying away, 

 is far from rare among the perennial herbs with short, tufted 

 rhizomes. Another manner in which the young plant can be 

 kept near the surface of the ground is by the roots as 

 mentioned under Hemerocallis and Eticliai^is, where the roots 

 show a distinct wrinkling, depending on their ability to con- 

 tract, and this fact is also observed in several other mono- 

 cotyledonous plants, as well as among the Dicotyledoneae. 



In regard to the shape of the cotyledons there is quite a 

 considerable difference, but the case of Aralia spinosa with 

 unequal cotyledons seems to be very rare. A similar case 

 has, however, been observed by Lubbock," who has described 

 the germination of Petiveria octandra. The cot}^Iedons were 

 different in size, and of a very different shape, one being 

 oblong, tapering at both ends and entire, while the other one 

 was subcordate and three-lobed. 



If we consider the figures, illustrating the germination of 

 the monocotyledonous plants (Plate XIII to Plate XIX), we 

 shall see that the germination is very uniform, although it 

 shows a few differences. The shape of the single cotyledon 

 is different, depending on the seed being albuminous or exal- 

 buminous. In the first case, it may be perfectly leaf-like, as 

 Agave and Alisma, or the superior part of the blade may be 



* Sir John Lubbock: Phytobiological Observations. Journal of Liiuu 

 Society, Vol. XXII, 1887, p. 371. 



ik. 



