ANATOMY OF THE GYMNOSPERMS 



variation in different species. In T. canadensis the spirals are 

 conspicuous throughout. In T. floridana they usually disappear in 



the later growth, and are wholly wanting 

 in the two or three last-formed tracheids. 

 In T. brevifolia they become very imper- 

 fect in the outer summer wood and tend 

 to disappear completely, only vestiges 

 remaining in the last-formed tracheids. 

 In T. cuspidata the spirals are generally 

 absent from the summer wood, or when 

 present are merely vestigial. The angle 

 is somewhat greater about 7 degrees 

 - than in Torreya, and with respect to 

 certain species this fact is apparent with- 

 out special measurement. The four spe- 

 cies appear to be paired off in such a 

 way as to represent a mean difference of 

 about 10.9 degrees as between T. cana- 

 densis and T. floridana on the one hand, 



FIG. 2. TAXUS BREVIFOLIA. and T " brevifolia and T. cuspidata on 

 Radial section showing the other. In all cases the angles of 



spirals of tracheids and the j rals are j te distinct from those 

 bordered pits, x 210 



of the lines of striation. The follow- 

 ing details are based upon an average of ten determinations : 



A comparison of these results in detail emphasizes the fact 

 that the distribution of the spirals, as between spring and sum- 

 mer wood, is in direct harmony with the principles already 



