9o8 



A TEXTBOOK OF THEORETICAL BOTANY 



Wood anatomy has proved a very useful adjunct to systematic Botany and 

 is serving to supplement the ideas of classification and evolution based upon 

 external morphology. The features principally used for comparison are : 

 fibre types, distribution of the xylem parenchyma, type of perforation in the 



I 



B 



D 



Fig. 892. — Tracheids in homoxylous members of the Ranales, 

 Tetracentrou, Trochodendron, and Drimys. {After Bailey 

 and Thotnpson.) 



end walls of vessels and the presence or absence of " storied structure " in 

 the wood. The origin of storied structure has been explained under the 

 heading of Cambium. It implies a marked uniformity of length in each 

 series of tracheids and vessel elements, as seen in longitudinal section, so 

 that the wood appears to be built up of vertically successive layers, or storeys. 

 These characters are not always sharply marked and a good deal has to be 

 left to the judgment of experience in deciding systematic affinities on wood 

 characters. 



