94 



ANATOMY OF THE GYMNOSPERMS 



prevails, and which may be regarded as the fundamental form of 



the ray, is that of from one to many cells superimposed in a single 



series of varying height (fig. 27). Such one- 

 seriate rays are characteristic features of all the 

 investigated recent genera. In 30 per cent of 

 the genera there is a sporadic tendency to 

 a multiseriate form as expressed in the devel- 

 opment of rays which are two-seriate in part. 

 Such enlargement is not confined to any partic- 

 ular portion of the structure, and within the 

 limits of the same section it may arise at the cen- 

 ter or at either end. It is never found in Abies, 

 Picea, or Pinus,but it is met with in Pseudotsuga 

 macrocarpa, three species of Cupressus, two of 

 Juniperus, one each of Sequoia and Araucaria, 

 and two of Larix (figs. 27, 

 28). In Libocedrus such 

 tendency is much more pro- 

 nounced, and the rays may 

 be described as two- to 

 three-seriate in part. 



This feature is of so 

 sporadic a nature that 

 existing species afford no 

 satisfactory evidence as to 

 its origin or significance, 

 but reference to Cordaites 



tends to throw some light upon this somewhat 



obscure problem. In fourteen species of Cor- FlG - 2iS - TAXUS BREVI- 



. ^ FOLIA. Tangential 



daites, three of which are European (28, 606- view of a mec i u iiary 

 609), it is seen that the rays present four ray showing its two- 

 variants ranging from the strictly one-seriate "J** 

 form to one- to two-, rarely three-seriate. 

 The distribution is in the following percentage proportions : 



1-2, rarely 3-seriate 2 1.4 per cent 



FIG. 27. SEQUOIA 

 SEMPERVIRENS. 

 Tangential section 

 of a medullary ray 

 showing a typically 

 one-seriate ray of 

 broad form. X 280 



1-2, seriate 



14-3 



2-seriate in part 

 I -seriate 



50.0 per cent 

 14.3 " 



