LEAVES AND lilllZOME. 



113 



The leaves usually arise near tlie apical l)U(ls of the main 

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

 the leaves of preceding years are often to he found, altfrnatinj; 

 on tlie sides of the rhizome in reguhir successicjn, and showing 

 various stages of decay. The iirst of these (whicli is on the 

 opposite side of the rhizome from the hving leaf) was aUve the 

 previous year; the next (on the same side with the hving Icafi is 

 the leaf of the year before that; and s(j on. Fig. 47 sIkhvs an 

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



Fig. 47. (After Sachs.)— Branch of a rhizome of Pteri.% showing the apical 

 the stumps of a number of successive leaves (?', P, P, etc.), and a part of 

 rnizome (rh), r, root. 



bud (a.h\ 

 tho main 



developed; and the relics of tlie leaves of the ])receding years 

 are indicated at l\ 1% etc. ; r is the rudiment of next year's leaf. 



Internal Structure of the Rhizome. The rhizome is a nearly 

 solid mass, consisting: of manv different kinds of cells, united 

 into different tissues, and having a very complicated arrange- 

 ment. Its study is somewhat difficnlt. Nevertheless the ar- 

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

 attention, since it has many features which are characteristic <»f 

 the cellular structure of the stems of higher ])lants. AVe shall 

 first examine its more obvious anatomv as dis])lave<l in transverse 

 and longitudinal sections, afterwards making a careful micro- 

 scopical study of the cells and tissues. 



Seen with a hand-lens or tlie naked eye, a transverse section 

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



