150 ANATOMY OF THE GYMNOSPERMS 



what has been shown in the course of the present studies, and 

 in its more comprehensive and exact form it should read, " Those 

 genera which are usually devoid of resin passages in the wood, 

 but some species of which may nevertheless contain resin cysts 

 in the young and vigorous growth, later produce single paren- 

 chyma elements in the wood which contain resin." 



Taken by itself, this statement as applied to Sequoia and 

 Abies might be held to indicate that the growth of the first year 

 represents the most stable structural region of the entire stem, 

 in the sense that it embodies characters which are most fully 

 established, and that it will therefore embrace elements which 

 may be eliminated from the older parts, or which may be 

 replaced there by degenerate forms only. From this point of 

 view it would be necessary to regard the complex resin passage 

 as the primitive form of structure from which the cysts, groups 

 of cells, and isolated resin cells have been derived by a process 

 of progressive degradation. This view appears to have been 

 adopted by Jeffrey (24, 454), who supports his position by citing 

 the occurrence of resin passages in the vascular structure of 

 the peduncle of certain fossil Cycads, interpreting this to mean 

 that such structures represent a survival of features which have 

 been obliterated from the structure of the stem. Such a view 

 does not seem to be in harmony with the facts which our own 

 studies have brought out, to the effect that resin passages of 

 the type found in the xylem structure are in no sense primitive 

 or vestigial, since they are wholly wanting in the primitive gym- 

 nosperms, and their organization does not arise until a very late 

 period in the evolution of the higher forms. If our interpretation 

 of observed facts is correct, as applied to the origin of the resin 

 passages, it shows as clearly as one could well expect a pro- 

 gressive development from the isolated resin cell through various 

 phases of aggregation to the highest form of structure as found 

 in Pinus. That there is such a series cannot be doubted, and 

 we must interpret it in one of two ways, - - either as progressive 

 evolution or as progressive degeneration. To us the arguments 

 all seem to be very emphatic with respect to lending support to 



