ANATOMY OF THE GYMNOSPERM6 



COMPARISON OF THE PRINCIPAL VARIATIONS IN THE SERIAL ARRANGE- 

 MENT OF BORDERED PITS, BY PERCENTAGES 



With respect to specific differentiations it has already ap- 

 peared that the bordered pits may be employed with success 

 in Taxus and Torreya. In Cupressus this rule also applies to 

 C. pisifera and C. macrocarpa, both of which are distinguished 

 by having their pits in one row or pairs, while the remaining 

 seven species have strictly one-seriate pits. An instructive ex- 

 ample is afforded by Cupressoxylon Dawsoni. In this species, 

 which is of early Tertiary age (Lignite Tertiary), the pits are 

 typically two-seriate, being disposed in a very compact manner 

 similar to that found in existing Sequoias. But in a series of 

 eleven specimens it is clearly seen that two variants are repre- 

 sented, the second being a one-seriate form. These variations 

 are also found, as in the other Coniferales, to be directly related 

 to variations in the size and rate of growth of the tracheid. It 

 cannot be doubted, then, that C. Dawsoni is a more primitive 



