LEAVES AND RHIZOME. 



118 



The leaves usually arise near the apical buds of the main 

 axis or of the branches. Behind each mature leaf remnants of 

 the leaves of preceding years are often to be found, alternating 

 on the sides of the rhizome in regular succession, and showing 

 various stages of decay. The first of these (which is on the 

 opposite side of the rhizome from the living leaf) was alive the 

 previous year ; the next (on the same side with the living leaf) is 

 the leaf of the year before that; and so on. Fig. 47 shows an 

 example of this sort. The leaf of the present year, l\ is fully 



FIG. 47. (After Sachs.) Branch of a rhizome of Pteris, showing the apical 

 the stumps of a number of successive leaves (I-, Z 2 , Z 3 , etc.), and a part of 

 rnizome (rh}. r, root. 



bud (a.f)\ 

 the main 



developed ; and the relics of the leaves of the preceding years 

 are indicated at Z 3 , Z 4 , etc. ; Z 1 is the rudiment of next year's leaf. 



Internal Structure of the Rhizome. The rhizome is a nearly 

 solid mass, consisting of many different kinds of cells, united 

 into different tissues, and having a very complicated arrange- 

 ment. Its study is somewhat difficult, Nevertheless the ar- 

 rangement of the cells is definite and constant, and merits careful 

 attention, since it has many features which are characteristic of 

 the cellular structure of the stems of higher plants. We shall 

 first examine its more obvious anatomy as displayed in transverse 

 and longitudinal sections, afterwards making a careful micro- 

 scopical study of the cells and tissues. 



Seen with a hand-lens or the naked eve. a transverse section 



/ 



of the rhizome (Fig. 48) presents a white or yellowish back- 



