Miscellaneous. 425 



in form, structure, and functions, from the stem and branches, and 

 could not, homologically, be compared with them. The nerves of 

 the leaves did not all diverge at the same angle, neither did the 

 branches. These last were exposed to various influences during the 

 life of a tree, and in consequence diverged from the stem at various 

 angles in the different periods of growth. It was therefore a dream 

 of the imagination to hope to determine a typical angle of divergence, 

 when the plant was endowed with a considerable range of variation to 

 fit it for its place in the ceconomy of nature. 



Prof. Goodsir had listened to Dr. M'Cosh's paper with much 

 interest, on two accounts : first, because it appeared to him that its 

 author had, in endeavouring to reach one of the objects he had in 

 view, embodied another attempt to investigate the laws of organic form 

 by that precise or geometrical method, which can alone ultimately 

 elevate natural history to the platform of the perfect sciences ; and 

 secondly, because, although he could not admit all the conclusions 

 at which its learned author had arrived, he yet believed the paper to 

 involve a great truth. If he might be allowed to use the expression 

 in reference to a plant, the specific physiognomy of a tree, as a mass, 

 appeared to him to depend on the particular bulk, form, and grouping 

 of its constituent masses. Now, if the form and grouping does not 

 depend upon, it certainly involves, the mode of branching peculiar to 

 the species. Dr. M'Cosh had restricted himself to the investigation 

 of the law which regulated the latter ; but he had, and would meet 

 with, that apparently at present insuperable difficulty in all such re- 

 searches, viz. the variation within certain limits of the form of parts, 

 or of the whole of an organized body, according to the particular con- 

 ditions under which that part or that individual has been developed. 

 Prof. Goodsir suggested that Dr. M'Cosh might be more successful 

 if he would limit his inquiry to the law of ramification of a single 

 judiciously-selected species ; and would endeavour to grow that species 

 under such invariable conditions as might afford an approach at least 

 to the typical form of the species. He also believed that before the 

 law which regulates the arrangement of the primary and secondary 

 ramifications of a leaf can be ascertained, attention must be directed 

 to the law of form in the parenchyma itself. 



MISCELLANEOUS. 



On Parasitism. By M. Leon Dufour. 



Parasitism seems to be a law of nature, so generally does it prevail 

 throughout the living world. This existence imposed in the creation 

 upon other existences is at once a law of antagonism, of repression, 

 and of guarantee for the maintenance of the harmony of nature. The 

 attentive study of the articulated animals, and particularly of insects, 

 presents to us the prodigies of parasitism in profusion, whether the 

 lens examines the integument of the animals, or the science of the 

 scalpel steps in to sound the depths of their organism. 



I have already had the honour to present to the Academy the 



