692 



THE AMERICAN NA TCRALIST. [\'ol. XXXVIIl. 



through the entire longitudinal growth of the season, at least. 

 There is no obvious alteration either in the position or volume 

 of the resinous contents of the isolated resin cells which lie on 

 the outer face of the summer wood. The constancy with which 

 these structures occur gives to them a definite value for the 

 recognition of the species, and permits us to differentiate it from 

 T. caroliniana on the one hand and from the remaining three 

 species on the other. 



In the genus Abies only four species out of elev^en show resin 

 cysts. These are A. bract cat a, A. nob His, A. cone lor and A. 

 firma. Referring again to Prantl's observation (44, p. 37), it 

 must be pointed out that his statement with respect to the 

 occurrence of resin passages in A. firma requires modification 

 in detail, in so far as these structures are not passages but cysts ; 

 while he also appears to have overlooked the occurrence of simi- 

 lar structures in the three other species mentioned. In all of 

 these cases the cysts are contiguous and disposed in tangential 

 rows of considerable length, either in the summer wood (^A. con- 

 color zxA A. nobilis), in the outer spring wood {A. firma), or in 

 both the spring and summer wood (^A. bracteata). Such varia- 

 tions appear to be of no specific value, conforming as they do to 

 similar variations in the zonate distribution of the resin cells. 

 It is found, however, that in only one case {A. concolor) are these 

 cysts associated with isolated resin cells. In the three other 

 cases the resin cells are entirely wanting, a relation which is 

 strongly suggestive of their replacement by the cysts. 



Sequoia scmpervircns is the only species of that genus which 

 develops resin cysts in the secondary wood, though Jeffrey (24) 

 has shown that such structures are normal to the primary wood 

 zone of 5. gigantea, and not elsewhere. As already shown, such 

 cysts are much more highly organized than those of either Tsuga 

 or Abies, though they are similarly contiguous and even coales- 

 cent, and form extensive tangential rows in the initial layer of 

 the spring wood of distant growth rings. They form a much 

 more prominent feature than in any of the preceding species, 

 because of their generally larger size and the greater extent of 

 the series in which they lie. Unlike Abies, however, there 

 appears to be no diminution either in the number or the extent 



