816 
were formerly occupied with the subject, 
_ which is unquestionably one of the most 
Important connected with practical bo- 
tany. .. 
To these important labours, M.de Can- 
dolle, has added three memoirs, which 
were presented to the class, during the 
Jast half year. 
In the first, he treats of the parasitical 
mushrooms, which are evolved under the 
epidermis of vegetables, and which fre- 
quently produce fatal diseases among se- 
veral usetul plants; the rust and" smut, 
which destroys oats, and the cartes which 
vitiates wheat, are probably attributable 
to this cause. Jt has hitherto been sup- 
posed, that these mushrooms were iiro- 
duced by the pores of the epidermis, bat 
as coloured liquors do not pass through 
these pores without great difficulty, and 
as simple contact has been found insufti- 
cient to nmpart these diseases to a_heal- 
thy plant, ‘M. de Candoile is of opinion, 
that their germs are introduced by the 
roots along with the nutritive juices which 
support the vegetable, and that they cir- 
culate through the vessels, till they reach 
those places best calculated for their de- 
velopement. He compares them in this 
respect to intestinal worms, which can 
only subsist in the interior of the body of 
manand other animals. From this theory, 
and from the observation tiiat each spe- 
cies of parasitical mushroom can only 
propagate itself in plants of the same fa- 
mily, he deduces rules, from which the 
agriculturist may deri ive great advantage, 
in stopping this kind of conta: x10N. 
Previous to the labours of MM. Candoile, 
we were acquainted, with sixty 
these mushrooms, which by his observa- 
tions, have been increased to one hun- 
dred. 
laa Memoir upon Marine Alge,he de- 
monstrates, that these plants are not fur- 
nished with real roots: that no trace 
whatever of vessels is discoverable in any 
part of their structure; that they absorb 
humidity by their wh ‘ole surface; and 
that they liberate oxygen gas, when ex- 
posed to light, in proportion to their green 
colour. He aleé asserts, that. the small 
rains, hitherto regarded as the seeds, 
are only the cap ssules, and contain grains 
much smaller, covered with a viscous 
matter, which fixes them in. situations 
adapted for their germination. Lasily, 
M. de Candolle has presented a botani- 
eal memoir upon the fa amily of the rubi- 
uccz, which he divides into four orders, 
and to which he adds four new genera, 
Proceedings of Learned Societies. 
v-four of 
(Nov. 1, 
M. Cuvier next proceeds to inform us, 
that M. de Petit-Thouars, who resided a_ 
long time in the Isles of France and Bour- 
bon, and likewise undertook a voyage to 
Madagascar, has begun to publish a Flora. 
of this iast island, which abounds in sin- 
gular plants. In “particular, he has col- 
lected some’valuable observations on the 
orchiedia, a tvibeof plants, which must be 
examined during iife, and which would. 
appear to be wholly unsusceptble of cul- 
tivation. He has a’ great number of new 
species of these plants ready for publica- 
tion. The ferns have also beena pecu- 
liar object of his research; the island of 
Madagascar alone furnished eighty-nine 
new genera, the characters of which he 
is about to present to the public, and 
which were sent by him to France, more 
than ten years ago. His observations on 
the germination of the cycas discovered 
to him that this singular tree, which was 
by some considered to be a fern, and by 
others a palm-tree, ought to constitute a 
‘distinct family. 
An exainination of the candle-wood 
(dracena), furnished him with particular 
facts extremely curious, and which led 
him to the adoption of a new and general 
system respecting the growth of trees, 
of which M. Cuvier presents us with the 
following account :— 
It is well known that the bark of trees 
in general, is augmented from the layers 
of wood, which are annually produced 
under the | bark, and that it 1s elongated 
and ranufied by shoots, which are merely 
the developement of buds. Each of 
these new shoots is composed of only a 
single layer of wood, which communi- 
cates with the last of those produced in 
the trunx, while the medulla, occupying 
the axis ot these shoots, proceeds from 
the pith in the centre of the tree. Na- 
turalists generally suppose that these 
successive layers of wood are every year 
thrown of from the internal surface of 
the bark. 
Palin, and other monocotyledonous — 
trees, grow in a different manner; the 
new fibres aredeveloped in the axis, and 
not in the periphery of the trunk ;. they 
traverse the whole length of ves AXIS, 
and expand themselves ‘into leaves and 
flowers at the summit of the tree. 
Hence the reason, why the trunk of the 
pecs increases in such an imper- 
ceptible manner, particularly towards its 
base, and in generals preduces no 
branches. ° 
if. Desfontaines, our colleague, con-, 
tinues 
