20O 



ANATOMICAL EVIDENCE 



It appears, then, that the anatomical evidence is consistent with the 

 early existence of a small-leaved type of shoot in Vascular Plants. Com- 

 parative anatomists are practically unanimous in recognising the non- 

 medullated monostele as the primitive stelar type, from which the more 

 diffuse vascular types with medulla, and ultimately with separate strands, 

 or it may be a dictyostelic state, were derived. Translated into terms of 

 general morphology, this opinion indicates a primitive state where the axis 

 was structurally dominant in the shoot. The derivation of more complex 

 anatomical arrangements from the non-medullated monostele suggests an 



FIG. 101. 



Embryo of Lycopoithini cernuittii, after Tretib. j = .su>pensor. / = foot. r=root. 

 f0l=cotyledon. The numerous protophylls contain each .1 \.i^uhu >tiancl, which ii 

 however disconnected from the rest. 



increasing influence of the leaf in the shoot at large, which finds its anatomical 

 expression in various types of resolution of the stele into separate strands. 

 The general conclusions from anatomy thus appear favourable to a strobiloid 

 theory of the shoot, and lead us to contemplate a primitive condition, in 

 which the axis was the dominant factor and the appendages of subordinate 

 importance. And as this coincides with the story of individual develop- 

 ment of the leaf upon the axis in all normal shoots, that coincidence should 

 go far in supporting a strobiloid theory of the shoot in the sporophytc 

 generation. 



