244 M. Vauclier 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 juices, 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 chara that 
grows abundantly in the Lake of Geneva, and, from the use to 
which it is ^.pplied, 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 w^ fortunate in collecting, in the month of November, what 
he deemed the true seeds. These he preserved through the 
winter, and in the month of April following, had the satisfaction. 
