HYPERTROPIED LEAVES. 47 



of those studied is the vascular bundle sinorle in the adult leaf, 

 P. strobiis, while in the others, the bundles, which are two, are 

 widely separated. 



It appears that the structures of the primary leaves produced 

 upon shoots, already mentioned, has not been studied, but it 

 has been assumed to be the same as that of the true primary 

 (primordial of Daguillon) leaves of the seedling. 



There can be no doubt that the bud scales, and the scales 

 which subtend the fascicles of Piiius are reduced leaves. In 

 view of this fact it is of peculiar interest that we are able to 

 cause their return to the foliage condition, in that we have 

 clearly a case of atavism. Furthermore, the structure of an 

 hypertrophied scale-leaf, if we are right in regarding this as a 

 case of atavism, ought to furnish some clue as to the phylo- 

 geny of the genus. It is assumed in such an argument that 

 leaf characters are to be depended upon as a guide, and of this, 

 I believe, there can be little doubt, for it has been abundantly 

 shown that these characters are quite constant. This is espe- 

 cially true, I believe, as regards the position of the resin ducts 

 concerning which Engelmann wrote that it is ''so constant and 

 seems to be so intimately connected with the essential character 

 of the plant, that I venture to adopt it as one of the principal 

 characters for the subdivision of the genus." Let us turn to 

 the consideration of the facts and see whether we may gather 

 any conclusions from them. 



The staminate shoots have normally small, scarious scales, 

 in the axils of which in the upper part of the shoot, are pro- 

 duced the staminate cones. If these shoots are cut off, one, 

 two or perhaps three axillary buds on the upper end of last 

 year's shoot will develop. So far I have been able to get no more 

 than three buds to develop. These buds, when developed into 

 shoots, have leaves which are narrowly triangular in outline, 

 broader at the base, and tapering gradually from the base to the 

 apex, and are of various lengths. The longest leaf observed 

 measures 6 cm. From the axils of some of these leaves were 

 developed normal fascicles. The transverse section shows them 

 to be flattened above and ridged along the middle line below. 



