112 



THE BIOLOGY OF A PLAN1. 



whose branching rhizomes cross and recross, making the subter- 

 ranean network already described, p. 109. 



Origin of Leaves upon the Rhizome and its Branches. The 

 young plant of Pteris puts up a number of leaves (7-12) yearly, 

 but the adult generally develops one only, which grows very 

 slowly, requiring two years before it unfolds. Towards the end 

 of the first year it is recognizable only as a minute knob at the 

 bottom of a depression near the growing point. At the begin- 

 ning of the second year it is perhaps an inch high, the stalk 



D. 



ep. s.p.fb 



FIG. 46. (After Sachs.) Developing leaf, etc., of Ptfris. A, end of a branch show- 

 ing the apical bud and the rudiment of a leaf ; 7?, a rudimentary leaf ; C, a 

 similar leaf in longitudinal section, showing the infolded lamina (I), the attach- 

 ment to the rhizome, and the prolongation of the tissues of the latter into the 

 leaf; D, lamina of a very young leaf ; K, horizontal section through a growing 

 point which has just forked to form two apical buds. a.h. apical bud ; ep, epi- 

 dermis and underlying sclerotic parenchyma ; f.tt, flbro-vascular bundles ; I, 

 lamina ; r, root ; s.p, sclerotic prosenchyma ; x, an adventitious bud at the base 

 of the leaf. 



only having appeared. At the end of the second year the lamina 

 is developed, and hangs down as shown in Fig. 46, C. Early in 

 the spring of the third year it breaks through the ground, and 

 grows rapidly to the fully-matured state. 



