RESIN CELLS 



119 



PERCENTAGE DISTRIBUTION OF RESIN CELLS 



structures have been seen to be peculiar to Dammara, Araucaria, 

 and Abies, in which they occur only in certain species. In answer- 

 ing this question we cannot avail ourselves of evidence derived 

 from fossil plants, since it is, in such cases, of a negative char- 

 acter. Neither Cordaites nor Araucarioxylon affords definite 

 proof of the presence or absence of such structures, since they do 

 not appear in any of the published diagnoses, and our own studies 

 have not resulted in their recognition. If originally present, they 



