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 



