386 Proceedings of Philosophical Societies. {[May, 
ARTICLE X. 
Proceedings of Philosophical Societies. 
LINNZAN SOCIETY. 
On Tuesday, April 2, a paper by M. Decandolle was read, de- 
scribing two new genera belonging to the family of rosacez, to 
which he gave the names of kerria and purshia. ‘The first is a 
Chinese plant, which has been long common in our gardens, under 
the name of corchorus japonicus. The second is an American 
plant, first described by Mr. Pursh, as a species of Tigarca. 
At the same meeting a paper was read, describing a new species 
of potatoe growing wild in New Granada, in South America, at a 
very great height above the level of the sea. The Spanish Eccle- 
siastic who found it proposes to call it solanum papa. The potatoes 
are white, and round, and well tasted. The fruit is oblong, which 
seems to constitute the chief difference between it and our potatoe. 
GEOLOGICAL SOCIETY. 
Feb. 16, 1816.—A report by Dr. Granville on a memoir by M. 
Methuen, entitled Découverte de la Maniére dont se forment les 
Cristaux, was read. ! 
This memoir was transmitted in manuscript to Dr. Granville by 
M. Gillet de Laumont, who in a subsequent letter expresses his 
great confidence in the veracity of M. Methuen, the author of this 
remarkable discovery. 
The formation of capillary crystals of alum and of sulphate of 
iron on the decomposing surface of aluminous schist, in a situation 
where no moisture, except that dissolved in the air, had access, first 
directed M. M.’s attention to the subject.. In order to destroy or 
confirm his hypothesis, he removed from the surface of a mass of 
silico-calcareous rock all appearances of crystallization, covered it 
over with fragments of the same rock, and left it exposed to the air, 
After a few weeks, some points of rock crystal made their appear- 
ance; by degrees the pyramidal summits were formed, then the 
prism shot out, its bulk diminishing as the crystal became more 
transparent ; and at the end of 23 months six beautiful crystals of 
quartz had been formed, from-s to 2 of an inch in length, and 4 of 
an inch in diameter, the stone around them being proportionally 
excavated. Encouraged by this success, he procured several speci« 
mens of a compound rock, consisting of alalite, garnet, green 
idocrase, pyroxene, and amorphous pyrites, arranged them in a 
heap on the chimney-piece of his room, keeping them duly moist- 
ened, and after several weeks had the satisfaction of seeing crystals 
of all these substances emerge from the mass: first came forth small 
crystals of pyroxene, next, summits of alalite, then planes of garnet, 
and lastly crystals of idocrase and of peridot. 
