COXIFKRALKS ( PIXACEAE) 



229 



(Pteropsida) among i)terido])hytcs (\). g), and with ihcm it is asso- 

 ciated with large leaves. The contrast with Lycopsida (Lycopodiales, 

 etc.), with small leaves and no leaf gaj^s, is complete. Since the coni- 



w 



Fig. 257. — Pinus Laricio: a cube from the secondary wood, reconstructed from 

 three camera drawings and showing various features of coniferous wood; in trans- 

 verse section at the left a few rows of small thick-walled cells of the autumn wood 

 are shown, and at the right the larger thinner-walled cells of the spring wood; tr, 

 transverse section; /;-, longitudinal radial section; //, longitudinal tangential section; 

 m, medullary ray; /), bordered pit; s, simple pit; X400. 



fers are characteristically small-leaved forms, they have suggested to 

 some a phylogenetic connection with the Lycopodiales (30, 41. 53); 

 but the presence of leaf gaps associates them with the Filicales, and 

 indicates that thev have been derived from large-leaved ancestors. 

 The persistence of leaf gaps when leaves are reduced in size makes 



