M. Vaucher on the Fall of Leaves. 



he supposes to consist in a peculiar structure that obtains at 

 the insertion of the petiole with the stem. The fibres of the 

 petiole, instead of being a simple prolongation of those of the 

 stem, are, according to him, distinct from them. At the point 

 where the separation of the leaf occurs, there is only a sort of 

 approximation, or soldering, and not a real continuity of vessels. 

 This soldering is supposed to be produced by the interposition of 

 parenchyme between the two systems of vessels. As long as 

 this parenchyme is supplied with j uices, and retains its vegeta- 

 tive power, the adherence of the petiole is maintained ; but 

 when it begins to dry, the connection fails, and the leaf falls. 



As this hypothesis is made to rest on anatomical grounds, we 

 could have wished that M. Vaucher had exhibited something 

 like a demonstration of the structure of these parts. He men- 

 tions, indeed, the existence of a circular ring or rising, visible 

 exteriorly, at the place of junction of the petiole with the 

 branch ; but that this is caused by the interposition of cellular 

 tissue between the vessels of the stem and petiole, or by any 

 sort of soldering of the extremities of these vessels with one an- 

 other, we have no evidence. We incline rather to the old opi- 

 nion, that these vessels are truly continuous ; and consequently, 

 that whatever be the cause of the fall, it is accompanied by a 

 rupture of vessels. That a diminution or cessation of vegeta- 

 tive power in the part precedes this event, has been generally 

 deemed probable; though others, as M. Vrolick and Sir J. 

 Smith, consider the fall of leaves in autumn as a sloughing of 

 worn out parts, effected by the vital energy of the parts in con- 

 tact with them. 



In his memoir " sur les Charagnes," a species of char a that 

 grows abundantly in the Lake of Geneva, and, from the use to 

 which it is applied, called by the inhabitants " herbe a ecurer," 

 M. Vaucher applies himself to discover its fructification, and 

 correct the erroneous opinions of Linnaeus, Schmidel, Hedwig, 

 and Martin, with relation to it. To accomplish this object, he 

 observed with care the germination of its seeds, which none of 

 his predecessors had done- After many unsuccessful attempts, 

 he was fortunate in collecting, in the month of November, what 

 lie deemed the true seeds. These he preserved through the 

 winter, and in the month of April following, had the satisfaction, 



