74 



ANALYSIS OF THE SHOOT-SYSTEM OF FERNS [ch. 



that the forking of the axis may occur either with or without the departure 

 of an associated leaf-trace (57, p. 543, Text Fig. 7; also p. 544, Text Fig. 8). 

 The inconstancy of orientation of the leaf which may thus accompany 

 forking provides facts material for an explanation of the positions of those 

 buds which are ranked under (II) and (HI), and their possible reference in 

 origin to dichotomy. Almost any bifurcating Fern is apt to show unequal 

 development of the two shanks of the fork. Occasionally these may be equal, 

 as in the Frontispiece, and as shown by Velenovsky's drawings (50, Figs. 

 165 — 167). But various degrees of inequality may be recognised, and these 



Fig. 68. Sections from point of dichotomy of the rhizome 

 of various Ferns, showing the absence of uniformity of 

 relation of the "angular" leaf to the branches of the 

 dichotomy, i, ii, iii suggest that the minor branch is 

 axillary; iv, v, vi suggest that it would be dorsal to the 

 leaf. 1 = Pi'i/aea faUa^a (G.-V. Coll. 1222); \\ = Davallia 

 pinnata (G.-V. Coll. 883, 892); \\\ = Davallia temtifolia 

 (G.-V. Coll. 927); \v = Lindsaya reiiiformis (G.-V. CoW. 

 1000); V = Davallia pinnata (G.-V. Coll. 888) ; v\ = Paesia 

 viscosa. 



are often more pronounced as the parts become mature. The case of Pte- 

 ridinin, which has long been a subject of discussion, serves as a good example. 

 The young plant starts with a single axis bearing 7 to 9 alternating leaves, 

 spirally arranged, after which it undergoes distal and equal dichotomy, and 

 on both of the elongated shanks a leaf may be borne near to its base (Fig. 69). 

 The two branches burrow downwards into the soil, bearing leaves alternately 

 right and left: in the later phases of their development they also show 

 dichotomies, but with unequal shanks: the shorter of these commonly bears 



