300 PROCEEDINGS OF THE ACADEMY OF 



to variation, and liave been preserved in given directions and repressed in 

 otliers, by tlie operation of tlie law of Natural Selection. (Darwin.) 



II. Genera have been produced by a system of retardation or acceleration 

 in the development of individuals ; the former on preestablished, the latter on 

 preconceived lines of direction. Or, in other words, that while nature's series 

 have been projected in accordance with the law of acceleration and retardation, 

 they have been limited, modified, and terminated by the law of natural selec- 

 tion, which may itself have operated in part by the same law. 



III. The processes of development of specific and generic characters have 

 not pvoceedeA pai-i passu, transitions of the one kind not being synchronous 

 with transitions of the other ; and that, therefore, species may be transferred 

 from one genus to another without losing their specific characters, and genera 

 from order to order without losing their generic characters. 



IV. And as the heterologous terms of the peculiar homologous groups pre- 

 sent an '' inexact parallelism " with each other ; and as types related by inexact 

 parallelism are each among themselves exact parallels in separate series, whose 

 earliest members present "exact parallelism" with each other, it follows — 



v. That the heterologous terms or genera in the later series are modified 

 descendants of those of the earlier series; in other words, that certain groups 

 higher than genera are produced from others of similar high value by " descent 

 with modification." 



VI. That the result of 'such successional metamorphoses will be expressed 

 in geologic history by more or less abrupt transitions, or expression points, 

 rather than by uniformly gradual successions. 



Of course, under the conclusion stated in Proposition II, the genus Homo 

 has been developed by the modification of some preexisteut genus. All his 

 traits which are merely functional have, as a consequence, been produced 

 during the process. Those traits which are not functional, but spiritual, are 

 of course amenable to a diiferent class of laws, which belong to the province 

 of religion. 



Variations in Taxodium and Finns. 

 BY THOMAS MEEHAN. 



In some remarks before the Academy on July 14th, in reference to adnation 

 in the leaves of Coniferae, I said that the power to branch was the test of vigor ; 

 and with increased vigor came proportionately the power of adnation. I 

 pointed out that this was the universal law through all Coniferae, so far as I 

 had been able to examine them ; and that it fully accounted for the specific 

 identity of many forms supposed to be distinct. I went so far as to suggest 

 that Tajoiit/m dixtichum. Richard, and Gli/ptostrobus sinensis, Eudl., were no 

 doubt the same thing, because the only difference between the growing plants 

 was in the different degrees of adnation in their foliage ; and because with 

 this adnation was the increased power to branch observed in all other cases. 

 The two points, going along together, seemed to indicate that this could not 

 be a solitary exception to so clearly marked a law. I exhibited specimens 

 taken from Taxodium, and from Glyptostrohus, showing the approach of the 

 two in the manner the theory indicated. 



Since then some new facts have come before me confirming this view in a 

 remarkable manner. On the nursery grounds of Mr. Roltert Buist, of the 

 Darby Road, near Pliiladelphia, are a few trees which I supposed to be the 

 Gh/ptostrobvs, but which Mr. Buist assured me were many j^ears ago, selected 

 by him from a bed of some thousand Taxodium on account of their peculiar 

 appearance. I exhibit specimens from eleven diflFerent trees. It will be seen 

 the suppression of the leaf blades or adnation is in exact proportion to vigor, 

 or the power of forming branchlets, and with this increased vigor the Taxodi- 

 um become Glyploslrobus, so far as any comparison of leaves and branches 

 can identify anything. 



[Oct. 



