128 IODINE CURIOUS PHENOMENON. [BOOK i. 



passes afterwards into violet or blue, even before the evapora- 

 tion of the liquid. Membranes that are harder, more brittle, 

 and less distensible in water, on the contrary, assume, under 

 the action of iodine, a yellow or brown colour, and do not 

 show a trace of blue, after being dried and again moistened, 

 unless a great quantity of iodine has acted upon them. 



3. The development of a blue colour is an attribute of the 

 cellular membrane itself, and may be caused by the absorp- 

 tion of a sufficient quantity of iodine. 



It is for chemists, says Professor Mohl, to say whether 

 iodine colours cellular membrane by merely interposing 

 itself between the particles of that membrane, or whether 

 iodine and woody fibre form determinate chemical combina- 

 tions, of which one is yellow and the other blue.* Be this as 

 it may, we cannot but regard these observations of the highest 

 interest to all engaged in the study of Vegetable Physiology. 



In connection with this subject we have a very singular 

 phenomenon recorded by Karl Muller, as having been observed 

 by him while examining the contents of the spore cells of 

 Lycopodium denticulatum. " When I treated these cells with 

 iodine, ether, and hydrochloric acid, I found that their deep 

 indigo blue colour was changed, and they became reddish, or 

 even wholly colourless. When I then touched the fluid in 

 which they swam, the slight agitation instantly restored the 

 blue colour. In a state of rest, however, this soon disappeared 

 again, and re-appeared when the fluid was touched, and so on. 

 But if the cells had become quite colourless, immediate con- 

 tact with some object, either of metal or wood, was necessary, 

 and then the blue colour again instantly seized upon one 

 point it appeared to me to be the nucleus and extended 

 itself over the whole cell. I have met with this remarkable 

 phenomenon in two spores. In spite of every endeavour I 



* The yellow appearance is explained upon the supposition that there exists 

 a slight, but real modification of starch, to which the name of AMYLOID has been 

 given. Schleiden regards it as an intermediate state between cell-membrane 

 and starch, found in the cotyledon cells of some plants, Schotia speciosa, Tama- 

 rindus indica, &c. It is cartilaginous while dry ; gelatinous when moist ; solu- 

 ble in boiling water, strong acids, or alkalies ; insoluble in ether or alcohol. 

 When moderately firm, it is coloured blue by iodine, losing this colour and 

 becoming yellow by soaking in water. (Henfrey). 



