No. 448.] NORTH AMERICAN CONIFERALES. 265 



The orifice of the pit is variable, at different 

 round, when the pits are also round and more 

 or less distant ; oval or oblong, when the pits 

 assume corresponding forms ; or in the summer 

 wood, lenticular or oblong. The transversely 

 elliptical pits of Finns strobus (Fig. 8), the ori- 

 fice of which is also transversely oblong, as also 

 the similar pits of Pinus cubensis (Fig. 7), afford 

 substantial proof in confirmation of the probable 

 correctness of this view. In the summer wood, 

 the pit orifice commonly assumes a position 

 which appears to offer a direct contradiction of 

 this conclusion. In Pimis strobus (Fig. 9), the 

 orifice is oblong and parallel with the tracheid 

 axis. In Pnms ptmgens, as in many others of 

 the same genus (Fig. 13), the narrow orifice is 

 extended above and below into a diagonal slit of ''^i.J^^ ""^ 

 great length, forming a narrow angle with the pits on t 

 tracheid axis. At first sight this would seem to rerlold, 

 imply that these features represent primitive 

 spirals, the original direction of which has not been greatl; 

 all modified, but one or two considerations will assist u: 

 correct interpretation of this feature. In the first place it 

 be observed that such positions and modifications of the 

 are invariably associated with the summer wood, or where 

 s the result of maceration ant 



they ar( 



I proces: 



always 1 



spicuous 



in those t 



experienced the most profound modifications with rcspc 

 growth in thickness of the secondary w^alls. It has aire; 

 shown in the case of Taxus and Torreya, that there is i 

 sary connection between the spiral bands and the spira 

 striation — that, as a matter of fact, as particular!}- il 

 by Torreya taxifolia, the two are quite distinct from ont 

 under ordinary conditions of development. But m cas 

 the wall experiences extreme growth in thickness, the 

 tion of the original spiral structure is complete, and at 

 time it is replaced by the normal striation of the wa 



