RESIN PASSAGES 



four species which develop cysts only one shows isolated resin 

 cells, and it is probably correct to interpret the variations noted 

 as expressions of developmental phases in such a way that the 

 occurrence of cysts represents the highest position. The genus 

 Tsuga is closely related to Abies in the occurrence of isolated 

 resin cells on the outer face of the summer wood, as also in the 

 formation of resin cysts, but it obviously occupies an inferior 

 position because (i) of the greater abundance of resin in the 

 individual cells, and (2) the occurrence of definite aggregates of 

 resin cells without the formation of cysts. This series is directly 

 extended by those genera in which definite resin passages re- 

 place the simple cysts, since the latter are convertible into the 

 former by easy and natural transitions. Both Pseudotsuga and 

 Larix occupy equivalent positions because they not only present 

 resin passages of an equal degree of development, but they also 

 show a survival of the isolated resin cells on the outer face of 

 the summer wood. Their affinities are therefore directly with 

 Abies and Tsuga on the lower side, but on the upper side their 

 alliance is with Picea, which presents a very similar though 

 somewhat higher organization of the resin passage and a com- 

 plete obliteration of the isolated resin cell. Yet again, the 

 structure of the resin passage in Picea at once connects that 

 genus with Pinus in which the most complete development is 

 attained, and it therefore terminates the series upwardly. 



Having special reference to the particular forms of the secre- 

 tory reservoirs, and leaving out of account all other considera- 

 tions than their particular evolution, it is possible to indicate 

 the general sequence of the genera, and, to a more limited 

 extent, of their species, as follows : 



i. Tsuga caro- 2. Abies bracteata. 3. Sequoia. 



liniana. Abies firma. 4. Pseudotsuga and Larix. 



Tsuga Mer- Abies nobilis. 5. Picea. 



tensiana. Abies concolor. 6. Pinus. 



From this it is manifest that Sequoia is superior to Tsuga and 

 Abies, but inferior to Pseudotsuga, Larix, etc. But if we now 

 view the general phylogeny with reference to the entire course 



