49 
also found that the embryo of Schotia latifolia is completely 
soluble in water, except the epidermis, and that this solution 
became blue by the action of iodine; wherefore he inferred 
that he had found a plant whose cellular tissue is in its natu- 
ral state all starch. 
Mr. Mohl’s object has been to pursue this enquiry with- 
out calling in the aid of re-agents. When the cells of the 
cotyledons of the Tropceolum majus are sliced thin and acted 
- upon by a concentrated tincture of iodine, they become a fine’ 
indigo-blue, but not suddenly; they are at first yellowish, 
and it is only after some time they become blue, and then it 
is by a transition through green, owing to the mixture of 
yellow and blue particles. In the mean while the primitive 
membranes remain yellow. But if such a slice is placed for 
a few seconds in strong caustic alkali, and is then washed in 
water, iodine then colours the cells at once of a clear indigo 
blue, and the primitive membrane acquires the same colour, 
but paler. The cells of Tropceolum are horny at first, and 
swell up when treated with water ; the same kind of texture 
occurs in Lichens, and Professor Mohl, in consequence, 
directed his observations to those plants. Although he did 
not meet with all the success he expected in the course of 
their examination, nevertheless he found that the shields of 
many species presented a similar phenomenon; for in many 
cases iodine produced a most beautiful indigo-blue both in 
the asci composed of primitive membrane, and in the inter- 
cellular substance that unites the cells. 
In examining the horny albumen of Endogens, several 
interesting remarks were made. The cells of which it is 
composed are generally very thick-sided, perfectly colourless, 
and are readily distended with water. When a slice of such 
albumen, previously softened in water, is exposed to the action 
of a concentrated tincture of iodine, the cellular membranes 
presently acquire colour; but it is not easy to describe in 
what way the changes of colour take place, because at first 
the iodine does not produce the colour which eventually re- 
sults from its prolonged action. In general it produces at 
first. a yellow colour, which by the intense action of iodine 
becomes brown; moreover this agent produces, in most cases, 
if it acts long enough, a blue colour. This blue is however 
never of the clear indigo tint that is observed, for instance, 
in the shields of Lichens, but it is always reddish, and of all 
