390 Proceedings of "Philosophical Societies. [Nov. 



leaves which ought to be the most delicate were the most capable of 

 resisting the action of the frost ; but it is net the frost which neces- 

 sarily occasions the fall of the leaf. That fall is a necessary effect 

 of vegetation ; and whether by the developement of the bud, or by 

 some other internal alteration prepared by nature, the footstalk 

 separates when the progress of its nutrition has brought it to the 

 point at which the tissue which served it as a connection is de- 

 stroyed. Accordingly when a tree dies from any cause during the 

 season of vegetation, the leaves continue to adhere. 



It is well known that various flowers open and shut at determinate 

 hours, and that heat and humidity have a great influence upon this 

 phenomenon. M. Desvaux, a botanist of Paris, has made obser- 

 vations on this subject on the mesemhrianthemnms, plants in which 

 these alternate motions are so remarkable, that their generic name 

 has been derived from it. He has found that the cause does not 

 reside in the corolla, as had been supposed, but in the calix, which, 

 in shutting, forces the corolla to obey its contractions; so that if the 

 calix be removed, the corolla continues expanded by night as well 

 as by day. 



M. de Mirbcl, our associate, has presented us this year with two 

 series of observations. The first on the seed, and on the mem- 

 branes which cover it ; the second on the pericarpium, or the 

 receptacle in which the seed is lodged. He has in the first place 

 examined how far the analogy pointed out by Malpighi between the 

 membranes which cover the foetus of animals in the matrix, and 

 those which cover the seeds of plants, is exact. The embrio con- 

 sisting of the plumula and radicle being considered as the foetus, 

 Malpighi considered the testa, or outer covering, to represent the 

 chorion ; and the tegmen, or interior covering, to represent the 

 amnios. The perisperme appeared to him to represent the liquid 

 contained in the amnios, in which the foetus swims. M. de Mirbel 

 finds, on the contrary, that at first the grain is merely a mucila- 

 ginous and continuous cellular texture, one part of which becomes 

 the embrio, and the remainder the perisperm and seminal tunics, 

 without its being possible to say that at any period the embrio swims 

 in a liquid. The mucilaginous state of this tissue, and its transpa- 

 rence, seem to have given occasion to the inaccurate comparison of 

 Malpighi. 



M. de Mirbel, passing to the examination of the pericarpium, 

 has succeeded in reducing its form under a general law, which, 

 determining what is essential in that part of vegetables, reduces 

 almost to nothing the anomalies which it appears to exhibit in 

 certain families. The general type of every pericarpium may in. his 

 opinion i e represented by a little box flattened at the sides and 

 composed of two valves, the union of which forms two edges or two 

 sutors, one more curved and the other more straight. To this last 

 sutor adhere the small seeds, and through it pass the vessels which 

 go to the seeds, either from the body of the plant, or from the 

 style or the organ which transmits the fructifying energy. This 



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