70 



THE BIOLOGY OF A PLANT. 



ing rhizomes cross and recross, making the subterranean network 

 already described, p. 67. 



Arrangement of the Leaves upon the Rhizome. 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 beginning of 

 the second year it is perhaps an inch high, the stalk only having 



D 



E 



ep. sp.fb. 



ct.b. 



FIG. 33. (After Sachs.) Developing leaf, etc., of Pteris. A, end of a branch showing the 

 apical bud and the rudiment of a leaf: B, a rudimentary leaf; C, a similar leaf in longi- 

 tudinal section, showing the infolded lamina (/), the attachment to the rhizome, and the 

 prolongation of the tissues of the latter into the leaf; D, lamina of a very young leaf; E. 

 horizontal section through a growing point which has just forked to form two apical 

 buds, d.b, apical bud; ep, epidermis and underlying sclerotic parenchyma; /.&, flbro- 

 vascular bundles; I, lamina; r, root; s.p, sclerotic prcsenchyma; jc, an adventitious bud 

 at the base of the leaf. 



appeared. At the end of the second year the lamina is developed, 

 and hangs down as shown in Fig. 33, C. Early in the spring of 

 the third year it breaks through the ground, and grows rapidly to 

 the fully matured state. 



The leaves usually arise near the apical buds of the main 



