554 



THE AMERICAN NATURALIST. [Vol. XXXVIII. 



Resin cells, when aggregated beyond a certaii 

 schizogenous, intercellular spaces which fori 

 closed cysts, or central canals of indetermir 



(a) the tracheids which provide nutrition for the s 

 cells ; 



(b) the secretory cells or epithelium in which the formation 

 of the resin takes place ; 



(c) the c t 1 1 11. provides an outlet or storage 

 reservoir for the surplus product ; 



(d) the thyloses which may impede the proper storage of 

 the resin, or which may individually serve the purpose of 

 storage. 



So long as the formation of resin is not excessive, it is stored 

 in the cells where produced. This is true of all isolated resin 

 cells, as well as of many which enter into the composition of 

 complex cysts and passages. When the resin is excessive, how- 

 ever, the surplus is excreted into specialized reservoirs of the 

 form of closed cysts, or of canals, and we are led to interpret 

 the appearance of these structures in the higher Coniferje as a 

 response to such needs. The development of the resin passages 

 will thus be seen to stand in direct relation to the capacity of 

 the plant as a resin producer — a fact which is otherwise ap- 

 parent from our knowledge of the general capacity of the differ- 

 ent genera as resin producers, and a comparison of this feature 

 with their known position in the line of descent. 



