1 1 2 ANATOMY OF THE GYMNOSPERMS 



group with which we are most particularly concerned at the 

 present moment, and as, with very few exceptions, they are 

 uniformly characterized by the presence of resin, which gives 

 them a distinctive appearance, I prefer to describe them as resin 

 cells rather than by the more commonly employed designation 

 of wood parenchyma, which conveys no suggestion of their 

 special function and most prominent feature. 



The resin cells are found to be entirely wanting in those 

 species of Taxus (4) and Torreya (3) which are included in the 

 present studies. They do occur, however, in Podocarpus, where 

 they present the usual structural features, but they are there 

 remarkable for their number and the great abundance of massive 

 resin which they contain. This distribution in the Taxaceae does 

 not altogether accord with the conclusions of Eichler (15, 35), 

 who states that they occur very sparingly in the Taxaceae, but 

 makes no mention whatever of their presence in Podocarpus, 

 where they are much too prominent to escape even the most 

 casual observation. 



In the Coniferac resin cells are characteristic of all genera 

 except Picea and Finns, where they are replaced by resin pas- 

 sages, of which they form essential parts. They are, therefore, 

 features in the wood structure of twelve genera, and they are 

 constant characteristics of all their species, with very few excep- 

 tions. Such exceptions apply exclusively to the genus Abies, 

 in which four species- -A. Fraseri, A. lasiocarpa, A. Veitchii, 

 and A. balsamea are wholly devoid of such structures. 



The recognition of the resin cells presents no difficulty in 

 the great majority of cases, because of the abundance and depth 

 of color of the resinous contents. This finds its most complete 

 expression in Taxodium, Sequoia, Cupressus, etc. In Abies, on 

 the other hand, where these cells have experienced extreme 

 numerical reduction, and where there also seems to be a cor- 

 responding reduction in their secretory power, it is impossible 

 to recognize them in this way. In such cases it is often pos- 

 sible to distinguish them by their slightly different form and 

 somewhat thinner walls as compared with the adjacent wood 



