10 
REPORT ON BOTANY, MDCCCXLI : 
seen, that the external strata of each cell were first loosened 
into a gelatinous mass ; and the cells, situated at the edge of 
the section, were entirely converted into a jelly, soluble in 
water. The dissolved substance, as well as the loosened 
membranes of cells, were beautifully coloured blue by iodine. 
The author next remarks upon the effect of iodine upon the 
cell-membrane in general, and draws the following inferences 
Is^, The iodine imparts very different colours to the vegetable 
cell-membrane, according to the quantity in which it is taken 
up by it. A slight quantity of iodine produces a yellow or 
brown, a larger quantity a violet, and a still larger quantity a 
blue colour. Iodine imparts the yellow or brown colour to the 
dried membrane of the cell, provided it is dissolved in alcohol, 
or otherwise comes in contact with the latter ; the violet or 
blue colour, on the other hand, only takes place when the cell- 
membrane is soaked in water. The blue colour converts itself 
into the violet or red brown upon being dried, but resumes the 
former colour on being again moistened; analogous changes 
of colour, as is well known, also take place with the iodine of 
starch, according to the circumstances of the latter being dry 
or wet. 2dly, The colour which the cell-membrane assumes 
through means of iodine, does not only depend on the quan- 
tity of iodine applied, but also on the quality of the membrane 
itself. The more soft and tender membranes, which swell 
readily in water, assume immediately a violet or blue colour, 
even when only a small quantity of iodine has been applied 
to them ; or the yellow colour, which they at first assumed, 
passes into a violet or blue colour, even before the fluid has 
completely dried up ; or, at all events, immediately after, and 
resumes it again on being soaked. The more hard, brittle 
membranes, which less readily swell in water, on the other 
hand, on the application of iodine, assume a yellow or brown 
colour; and, after being dried and soaked again, assume a 
blue colour, when a large quantity of iodine has acted upon 
them. Third, This development of a blue colour entirely de- 
pends on the nature of the membrane of the cell, and is only 
produced by the addition of a sufficiently large quantity of 
iodine. 
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