STEM 



25 



Fig. 41. 



arising on the primary stem is termed an axis of the second 

 order, or a secondary axis. A lateral axis (iii.) arising on a 

 secondary axis is an axis of the third 

 order, or a tertiary axis ; and so on. 

 Formation of false-stems or sym- 

 podia. — A simple stem being un- 

 branched obviously must be an axis 

 of the first, second, or third, etc. 

 order. Frequently, branched stems 

 are formed which, at first sight, seem 

 to be simple ; this is particularly the ■ 

 case in plants possessing stems of 

 definite growth. 



The formation of such a falsely 

 simple stem — a sympodium — may be 

 illustrated by considering the growth 

 of a grass which lives for several years and possesses a sub- 

 terranean shoot-system. Following out the development of a 

 horizontal under-ground stem of a grass, it will be seen that the 

 end of the stem eventually bends out of the soil, becomes erect, 



and terminates in an in- 

 florescence. But the base 

 of the erect portion of 

 this stem produces a bud 

 which grows for a certain 

 distance in the soil and 

 presents the false appear- 

 ance of being a continua- 

 tion of the original stem. ' 

 This lateral axis in turn 

 bends out of the soil and 

 produces flowers as did 

 the first stem. A third 

 axis arises on the second 

 ■ lateral axis and behaves in 

 exactly the same manner 

 as its predecessors. Fig. 

 42 is a diagram of a 

 grass which is supposed tq be flowering at the present time 

 (in summer). A year ago, axis i. bore flowers (which are now 

 invisible), and it also possessed a leafy branch (11.), the 



Fig. 42. — Method of growtli of a perennial 

 Grass. 



