87 



be taken into consideration. This is the distinct wrinkling, 

 which the primary root shows, and which may be observed 

 also in the secondary root, when it has grown out to its full 



length, as shown in Fig. 129. This peculiar fact (the wrin- 

 kling of the roots) depends on their ability to contract, and, 

 as explained by Irmisch, is for the purpose of keeping the 

 plant as close to the ground as possible. The older state ot 

 the plant, figured in Fig. 129, shows also that the secondary 

 root (r) has increased quite considerably in thickness, being 

 almost fusiform, taking the function of a nutritive root, and 

 contains a large quantity of starch, like the tuberous roots, 

 of Orchis, Dahlia and several others. 



Yucca gloria sa. 



The seed of this species is compressed, almost triangular, 

 with a corneous albumen. A longitudinal section of the seed 

 (Plate XVI, Fig. 131) shows the fusiform apex of the cotyle- 

 <^ don, lying diagonally in the albumen. When the seed com- 



mences to germinate the primary root is the first that appears; 

 it is rather thick and attains a considerable length before the 

 plumule becomes visible. Figs. 130 and 132 show this very 

 first stage oi the germination, and we observe there a slight 

 bending downwards of the cotyledon, so that the seed is kept 

 under ground during this, the first, stage of the germination. 

 The lowxr part of the cotyledon shows very early an incipient 

 swelling, which is caused by the growth of the plumule inside, 

 ^^g' 133 shows the plumule (P) coming out, but in other 

 regards the germinating plantlct has not changed from what 

 has been figured above. But after that time, when the first 

 leaf has been developed (L^ in Fig. 134), some very consider- 

 able changes have taken place. The primary root has 

 grown rapidly out, and shows already some lateral branches, 

 and the cotyledon has commenced to stretch itself upwards, ' 

 so that the seed is entirely above ground, still being for some 

 time carried by the apex of the cotyledon, the base of which 

 shows the swelling, mentioned above, and has even increased 

 in length. The first leaf alternates with the cotyledon, is 

 broadly linear, pointed and five-nerved. In the next stage 



-i 



