No. 449.] NORTH AMERICAN CONIFERALES. 341 



adjacent parenchyma cells, but they are always much smaller 

 than the pits of those wood tracheids on which they border. 

 Such tracheids are invariable features of the ray in all the higher 

 Coniferae from Tsuga and Pseudotsuga to Pinus to the extent of 

 25% of the investigated genera. In Juniperus they occur very 

 rarely, being found, so far as I am aware, in only one species 

 {/. nana) out of a total of eleven, and they are so sjDaringly de- 

 veloped ^s to readily escape observation. In Thuya they are to 

 be met with in T. japonica, likewise in a rudimentary state of 

 development. Out of nine species of Cupressus they occur 

 only in C. nootkatensis. Of the ten investigated species of 

 Abies, they are found only in A. balsamea. In commenting 

 upon this fact many years since, De. Bary (9, p. 490), also pointed 

 out that among European species A. excelsa is similarly excep- 

 tional, but no attempt has been made to interpret their signifi- 

 cance. In Thuya, Cupressus and Abies the tracheids are strictly 

 marginal in the composite rays, forming the entire structure 

 in rays only one or two elements high. This relation obtains 

 in all the higher Coniferae in the first instance ; but in Larix, 

 Picea and Pinus, where there is a notable increase in numbers, 

 they also become interspersed with the parenchyma cells and 

 eventually predominate over them, a feature which is especially 

 characteristic of the hard pines. Efforts have been made to 

 show that in all such cases the two kinds of elements succeed 

 one another in a definite order from above downward — or the 

 reverse — but our studies have failed to show that this is capable 

 of practical application to the purposes of classification, or even 

 of phylogeny (9, p. 491). The great fact of importance for our 

 present purpose, however, and one which stands out with much 

 prominence, is that the ray tracheids are not a structural feature 

 of the more primitive Coniferales, but only of the higher types 

 such as Picea and Pinus. Furthermore, the primitive position 

 for these structures is in the one or two-celled rays, or corre- 

 spondingly in the margins of the composite rays. 



In Thuya and Cupressus the tracheids appear to stand by 

 themselves, and they exhibit no special relations to the paren- 

 chyma elements which would permit of inferences as to their 

 possible origin. In the genus Pinus, on the other hand, where 



