454 Proceedings of Philosophical Societies. [Dec. 



filaments or branched ones, lives upon the roots of living plants, 

 attacks them externally, and destroys them by absorbing their 

 nourishment. These plants multiply with rapidity, by means of 

 their filaments, which spread from one plant to another, and occa- 

 sion contagious diseases, from which several of our cultivators have 

 suffered. Only one species is well known which produces the 

 disease, too famous in Gatinois, called death of saffron. Another 

 species, which M. tie Candolle describes for the first time, commits 

 its ravages on lucern. Its filaments, of a fine lake colour, firmly 

 embrace the roots of the lucern. The plants attacked droop, 

 become yellow, and speedily die; and as the mushroom propagates 

 itself in radii, we speedily see in fields of lucern circular spots 

 quite withered. The author advises to dig pits round the infected 

 spots sufficiently deep to prevent the red filaments from crossing 

 them, taking care to throw the earth from the pits into the circle, 

 that the evil may not be increased in attempting to remedy it. 



One of the greatest difficulties in botany consists in accurately 

 fixing the limits of the species, and in not considering as species 

 the varieties produced by the soil and the climate ; and the best 

 means of avoiding these mistakes is not to admit as specific cha- 

 racters those circumstances belonging to the organization whose 

 mutability has been ascertained. M. Desvaux, having applied this 

 method to the roses, and having observed that several of the pre- 

 tended species of this genus differ only in characters which fre- 

 quently vary in the same individual, has succeeded in greatly 

 reducing the nominal species of this plant. He has shown, for 

 example, that the common wild rose (rosa canina) exhibits 21 

 varieties, all of which admit of being described, but which pass 

 insensibly from the one to the other : 13 of these varieties have 

 been improperly elevated to the rank of species by certain authors. 

 Six other pretended species are likewise deprived of that rank, and 

 brought under the rosa alpina, five under the hedge rose, &c. The 

 same severity introduced into the whole of natural history would 

 simplify and elucidate it very much. But for that purpose it would 

 be necessary for naturalists to employ themselves in critical re- 

 searches, and to renounce the vain honour of increasing without 

 end the number of species, in the present state of the science 

 there would certainly be more trouble, more utility, and more 

 glory, in diminishing that list. 



M. Delille, Member of the Institute of Egypt, has read to the 

 Class an interesting history of the wild and cultivated plants in that 

 famous country. He intends it as a part of the great general work 

 on Egypt, to which so much talent concurs, and which is publishing 

 with a magnificence corresponding to the greatness of an cnterprize 

 of which it will be the most durable monument. The author dis- 

 tinguishes the plants peculiar to Egypt from those brought by the 

 inundations of the Nile and the winds of the desert, and from 

 those common to it and the neighbouring countries. He fixes the 



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