RESIN PASSAGES 



127 



In Tsuga caroliniana there are no secretory reservoirs, but 

 just in the region between the spring and summer wood of the 

 same growth ring there are peculiar 

 aggregates of resin cells of a more 

 or less rounded outline, forming a 

 continuous series of considerable 

 extent. An analysis of these aggre- 

 gates shows them to be composed of 

 thick-walled and rounded resin cells, 

 among which there may be a small 

 central, intercellular space without 

 any definite organization of epithe- 

 lium. In such aggregates the com- 

 ponent cells are far less resinous ep.. 

 than the isolated resin cells of the 

 same section. The parenchyma tra- ep.- 

 cheids are not clearly distinguishable 

 from the associated wood tracheids. 

 In radial section the cells are seen 

 to be very variable, thick-walled, and 

 sometimes with more or less promi- 

 nent intercellular spaces. Between 

 the rays they are several times longer 

 than broad, but opposite the rays 

 they are short, cylindrical, and more 

 copiously pitted ; while sometimes 

 they may be seen to merge into ray 

 elements and thus to continue their 

 course at right angles to their pri- 

 mary direction. A careful compari- FIG. 41. SEQUOIA SEMPERVIRENS. 



son Of these cell aggregates with Radial section of a resin cyst 



showing the epithelium (<?/.) and 



those of Sequoia and Abies leaves the thyioses (///.), which com- 

 little room for doubt as to their struc- P letel y fin the c y st ' and several 



.... of which are resinous. X 225 



tural and functional identity, and we 



cannot do otherwise than conclude that they represent the most 



primitive structural condition which is capable of directly giving 



