3« 



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 

 ■i\ "" . 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 



F.G. .8 -Gemunation of Indian corn (Z.. «,.»): successive ages,/,//, plant Is Ouly tO bc UUdcr- 



///. A and B the seedling removed from /, witli its scutellum sc. Every- (.(-nnH if tVlP'JP mnffprn n rp kpnt 



where, w primar>' root; ifs root sheath; -W. a" secondary roots; * first StOOQ H tnebC maUCrS are KCpL 



leaves; k first segment of slioot-axis ; r edge of scutellum; e endosperm, • vMp,y 



surrounded by the pericarp (nat. size. Cf. Fig. 5). "' View. 



