No. 449.] NORTH AMERICAN CONIFERALES. 



present four variants ranging from the strictly uniseriate form to 

 I -2-, rarely 3-seriate. The distribution is in the following per- 

 centage proportions : 



I -2-, rarely 3-seriate 21.4;^; 



1- 2-seriate 14.3 ^; 



2- seriate in part ^o.of 



I -seriate 14.3 % 



From this it would appear that Cordaites as a whole, 

 approaches the primitive, multiseriate ray such as may be found 

 in the Cycads, much more nearly than any of the existing 

 species under consideration, and from this point of \icw it 

 becomes possible to arrange a sequence showing the relative 

 development in the following terms: (i) Cordaites, (2) Libo- 

 cedrus, (3) all other genera as 

 enumerated above. The evi- 

 dence of fossil plants, how- 

 ever, shows that caution must 

 be exercised in our estimate 

 of what constitutes the primi- 

 tive ray. The structure of 

 Stigmaria shows a preponder- 

 ance of uniseriate medullary 

 ^ays (51, P- 224) and that 

 such are primitive rays cannot 

 well be doubted. In general, 

 however, we are probably not 

 far from correct in the assump- 

 tion that the highest form of 

 the ray is expressed in its uni- 

 seriate character. Deviations 

 from this would then require 

 to be interpreted as vestigial 

 features which indicate a rela- 

 tively lower type of organiza- 

 tion in direct proportion to the ceiis. x 410. (b) xransve 

 increase of a tendency toward rptolt'^trS'eil°'''x^3^^^^^^ 

 a multiseriate form. 



In the majority of species, the side walls of the \ 



