m 



38 LECTURE IV. 



their aerial parts branch-systems which have become developed from the original 



germinal shoot (Plumule) of the seed. 



As already indicated above, a typical shoot consists of the leaves and the shoot- 

 axis, which are, however, in the 

 first place' not properly to be 

 considered as different organs, 

 but essentially only as por- 

 tions of one organ, although, 

 by peculiar development and 

 further formations later, the 

 leaves as well as the shoot- 

 axes may assume distinctive 

 characters. Essentially, and as 

 the history of development 

 shows, the leaves are how- 

 ever, strictly speaking, nothing 

 more than protuberances or 

 out-growths of the shoot-axis, 

 which, by means of their large 

 development of surface, are qua- 

 lified to present the chlorophyll 

 contained in them to the light, 

 and to the air containing car- 

 bon dioxide, in the most ap- 

 propriate manner, so that 

 the process of assimilation, the 

 production of organic substance 

 for the whole plant, may take 

 place with the greatest possible 

 energy. In this connection, the 

 shoot-axis appears first only in 

 the simple character of a sup- 

 port, on which these organs 

 of assimilation are suitably 

 arranged in large numbers. 

 The products of assimilation 

 are also conducted upwards 

 as well as downwards in 

 it; while at the same time 

 water and nutritive matters 

 are conveyed from the roots 

 to the leaves through it. The 

 whole structure of a higher 



r,,'^'5' '''~''°""'"'"'°" °'^'"'''" '=°™'-^"""''"'= ^^^'issiveages, /, //, plant is Only to be under-' 



///. A and B the seedling removed from /, with its scutellum sc. Every- j -r 1 



where, w primary root; ws root sheath; -w'. »" secondary roots; b first StOOQ it thcSB mattCrS are kept 



leaves; i first segment of shoot-axis; >- edge of scutellum; e endosperm. ■ . 



surrounded by the pericarp (nat. size; Cf. Fig. 5). IH VieW. 



