EXTRACTS FROM FOREIGN PERIODICALS. 
101 
Turned back on its external face, and this face being charged with pigmentum, 
the membrane obtains, on its internal surface, a bluish tint; deprived of the 
pigmentum, it is yellowish. The cellular or areolar membrane is also of a yel¬ 
lowish hue, but less intense. The epidermis is ash-coloured. The dermis alone 
is white. 
I have already said that the pigmentum is only a single layer, a covering, a 
deposit, and not a membrane. 
The membrane which covers it is a true continuous membrane. It is the in¬ 
ternal layer of the cuticle. 
M. Flourens has discovered all these parts in the skin of the negro and the 
mulatto, and has succeeded in obtaining them by macerations more or less pro¬ 
longed. 
In white men this dissection is much more difficult. M. Flourens has there 
found a double epidermis, but all his endeavours to discover a mucous body 
have been in vain. Whether this mucous body is wanting in the white race, 
whether the maceration should be conducted in a different manner, or replaced 
by another process, he has failed in discovering between the dermis and cuticle 
any other layer than the membrane of the internal epidermis .—Bibliolheque 
Universelle de Geneve, premiere Annee* 
BOTANY. 
3. Sleep of Flowers. —-In our last number (Yol. III., p. 42) we left M. 
Dutrochet advancing the following statement:— 44 It might be concluded, since 
the expansion of the flower is owing to the turgescence of the cellular tissue of 
its nerves, that its closing or its sleep was due to depletion of the same cellular 
tissue: but experience proves that such is not the cause of the sleep of the 
corolla.” We now proceed to supply his reasons for the above statement. 
I separated a nerve of a corolla about to expand, and immersed it in water. 
This nerve (curved slightly inwards, as in the corolla while in bud) is powerfully 
forced outwards—the mode of incurvation which effects the expansion. Endos- 
mose, then, determines the turgescence of the cellular tissue, the organ of this 
incurvation. After an immersion of about six hours the nerve ceased its outward 
curvation, and began to curve inwards; in a short time it was entirely rolled 
spirally in this new direction, that of incurvation, to which is due the sleep or 
closing of the flower. This succession of phenomena is altogether independent 
of the action of light. Thus the nerve of the corolla of Mirabilis takes in water 
the incurvation which effects the sleep of the flower, and it then takes, after a 
certain time, the incurvation which causes the opening of this same flower. If, 
then, it is the turgescence of the cellular tissue of the nerves that produces the 
incurvation to which the expansion of the corolla is owing, the incurvation to 
p 2 
