PROTOPLASM THROUGH THE WALLS OF VEGETABLE CELLS. 
825 
mounted in Chlor. Zinc Iod. The cel]-wall is coloured yellow ; the protoplasm and the 
protoplasmic threads a dark brown. The success of the reaction depends upon the 
fact that when cellulose has experienced a loss of water, and has become dry as in the 
case of ripe endosperms and other dry tissues, the Chlor. Zinc Iod. will not at first 
give the usual blue coloration. It is only after some considerable time that the section 
will begin to turn blue, or if the cell-wall be very thick or very dry, the blue colour 
may not be produced at all, but only a yellow brown, which is frequently increased in 
depth by the precipitation of iodine attending such lengthy action. Sections of a 
germinating seed of Phytelephas furnish an excellent proof that the assumption of the 
blue colour on treatment with Chlor. Zinc Iod. depends upon hydration, for whereas 
the normal cells will give a yellow colour, those which are being encroached upon by 
the absorbent foot of the growing embryo, and are being broken down and at the same 
time thoroughly wetted, will give in a peculiarly characteristic manner the customary 
blue cellulose reaction. 
But usually in sections of ripe endosperms the cell walls become yellow, and the 
protoplasm colours dark brown. In most cases nothing can be seen at first of any 
threads in the cell-wall, but after some time (varying from a quarter of an hour to one 
hour) they gradually come into view and are moreover apparently increased in size by 
the gradual precipitation of iodine upon them due to the action of the Chlor. Zinc Iod. 
One great objection to this method is that when fresh tissue or thin walled tissue 
is used, the ordinary blue cellulose reaction occurs which totally obscures the threads 
from view, and makes all observation of no avail. Moreover, no permanent prepara¬ 
tions can be made. My first idea was to employ the same modification as I had 
adopted in the case of sulphuric acid and use Hofmann’s blue instead of iodine. 
With this, however, I at first experienced some difficulty. Tan Gin found in Strychnos 
that when he had swollen the walls with water and could see the threads with dilute 
iodine solution, he was unable to stain them with any ordinary dye, such as hseina- 
toxylin or carmine. In the same way I found that after the action of iodine and Chlor. 
Zinc Iod. I could not succeed in staining the threads with any solution of aniline 
colours. In consequence of this I made a number of experiments with Strychnos. I 
found that although no dyes would demonstrate the threads, yet with solutions of such 
coloured bodies as gold chloride, picric acid, chromic acid, and iodine, they became 
more or less clearly apparent. It will be noticed that all these substances are well- 
defined crystalloids, whereas most of the aniline colours are inclined to be colloidal 
or, at least, are crystallised with some difficulty. This suggested that the whole 
phenomenon was simply a matter of diffusion, the solutions of crystalline bodies 
apparently permeating the substance of the cell wall (crystalloid), but especially 
diffusing into the protoplasm (colloid), and in the same way the solution of the colloidal 
aniline dyes diffusing but little or not at all into the colloidal protoplasm. In conse¬ 
quence of this conclusion I made the experiment of dissolving the solid Hofmann’s 
* Loc. cit. 
