8 
REPORT ON BOTANY, MDCCCXLI : 
other by the slightest application of force ; and this can only 
he done, when the attracting and repelling powers of the 
homogeneous parts neutralize each other, which cannot be 
the case on the surface of fluid substances, where the parts 
are unequally drawn in different directions. This solidity 
increases with the surface, and a thin stratum of fluidity is 
consequently in itself solid. The degree of solidity certainly 
depends on the degree of attraction among the parts, which, 
as is well known, is different also in fluid substances, as exhi- 
bited by quicksilver and water. Nothing, therefore, is re- 
quired, for the production of a membrane, hut the separation 
of a stratum of fluidity, as every bubble shows. The half 
fluid substances, mucus, jelly, &c., are a mixture of solid and 
fluid parts, as can be seen when they are dried, and it is 
saying nothing, to say we have derived a solid substance from 
mucus. Nor is it by any means necessary, that a fluid sub- 
stance should have to pass through a state of half fluidity, in 
order to become solid — as a proof of which, we may adduce 
the crystals of salt. If we admit attracting and repelling 
powers to act at pleasure, as M. Harting has done, a good 
deal may certainly be explained ; but we must divest our 
explanation, as much as possible, of arbitrary assumptions. 
We have received many researches this year respecting the 
chemical constitution of cellular tissue. First, Some obser- 
vations respecting the colouring blue of the vegetable cell- 
membrane, through means of iodine, by Hugo Mohl. Flora, 
1840, p. 609. In consequence of Schleiden’s observations, 
the author instituted researches regarding the embryo of 
Schotia speciosa. This embryo swells by a lengthened ma- 
ceration in cold water, and by boiling with water, but is not 
entirely dissolved ; and then, not only are the cells coloured 
blue by the application of iodine, but also the mucus around 
them. The cells of the cotyledons of Tropeolum majus, 
hyhridum, and minus, exhibit a similar reaction. The blue 
colour with them, however, does not appear immediately, but 
the cell-membrane first turns yellow, then green, and finally 
blue. The cell-membrane of many lichens was likewise ana- 
lyzed, after Meyen’s suggestion, and a similar reaction was 
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