1889.] NATURAL SCIENCES OF PHILADELPHIA. 57 



circumference of the branch year after year as the branch increases 

 in thickness, but rarely getting far enough forward to form " second- 

 ary" leaves ; in Pinus rig Ida manage in time to get beyond the bark of 

 the main branches, again become foliaceous, and produce a dense an- 

 nual crop of "needles" or secondary leaves along the whole surface. 

 This has not been noted on Pinus pungens, though it has the char- 

 acter of making vigorous and much ramifying side branches more 

 strongly developed. In many cases, the side-branches compete in 

 vigor with the leaders, till the tree loses the specific character of 

 most pines in having a distinctive trunk or leading stem, after it 

 has reached no great height from the ground. 



Another feature in which it agrees with Pinus rigida, is in the 

 habit of bearing flowers, both male and female, on comparatively 

 young plants. In the general characteristics of branches, foliage, 

 and cones, it is easy to see the general relationship to P. rigida. 



In one respect, however, there is a remarkable difference. Pinus 

 rigida, is, in its cones, among the most variable of Pines. In his 

 paper on " Variations in nature" read by the author of this before 

 the American Association for the Advancement of Science, at its 

 Montreal meeting, a series of cones was used in illustration showing 

 a complete line between P. rigida, P. serotina, and P. Tceda, the 

 changes being so gradual that, so far as the cones evidenced, no 

 line could be drawn between the three, distinct enough as they are 

 when the intermediates become " missing links." In the hills about 

 Lewistown, some trees of P. rigida, were noted with cones little 

 larger than good-sized Filberts. Pinus inops also varies very much 

 in the form of its cones. But Pinus pungens, owing its parentage, 

 as it probably does, to P. rigida, is remarkably constant in the size 

 and form of its cones. Of the hundreds of trees that I have seen in 

 the whole Allegheny range, from North Carolina to the Schuylkill 

 river, the cones seem uniform in size and other characters. 



In the unexpected appearance of a plant with which we are 

 familiar in another region, we not onlv look for similarity in the 

 geological features, but for companion plants as well. In the author's 

 memory, Polypodium incanum is associated growing on rocks and 

 trees with Pinus pungens in Virginia. It was natural to look for it 

 here, but only its ally, Polypodium vulgare, was to be seen. It is 

 possibly a low-land fern in its origin, pressing up iuto these higher 

 regions long after the exposure of the Silurian rock in these upper 



