THE WHITE LILY 197 



inner cortex is the actively contractile tissue; as it 

 contracts the external layers are thrown into trans- 

 verse wrinkles, as shown in Fig. 94. New roots of 

 this kind are formed each year, until the bulb has 

 reached its normal depth (three inches or more in the 

 case of L. Martagon). 



SUMMARY 



If we now shortly sum up those essential points in 

 the life-history of the Lily in which it serves as a 

 type of the Monocotyledons generally, we find that 

 the following are the chief : 



(1) In the external morphology the most striking 

 point is the predominance of adventitious roots, the 

 main root serving a merely temporary purpose, namely, 

 the nutrition of the seedling. The explanation of this 

 peculiarity is to be found in the mode of growth of the 

 plant as a whole. The main root is a slender struc- 

 ture, corresponding to the small dimensions of the 

 thin basal portion of the stem, with which it develops 

 simultaneously. Hence, as the stem becomes for a 

 time larger and larger in each successive node and 

 internode, the root becomes more and more inadequate 

 to supply its needs. The root has no secondary growth 

 in thickness, and therefore cannot make good its 

 deficiencies. Thus the requirements of the plant can 

 only be satisfied if the later-formed bulkier portions 

 of the stem produce new and larger roots proportioned 

 to the organs which they supply. 



(2) The primary bundle-system in the stem and 

 root is on the whole more complex than in Dicoty- 

 ledons, the individual bundles being more numerous, 



