156 
On the Staining of 
[Monthly Microscopical 
Journal, Sept. 1. 1869. 
cambium cells bounding this layer are quite colourless. In the 
outer layer of cambium the cells become large, more like the bark 
cells, and here and there a few bundles of thickened cells can be 
seen, brightly coloured like the others. These, I suppose, are bast 
cells. A few of the laticiferous canals, described last year in 
' Botanical Society Transactions,' are lying close to these small 
patches of bast cells, but far more frequently they lie close to the 
small cambium cells. The layer of cellular tissue, external to 
the bast cells, is not coloured, and their thin walls contrast strongly 
with the greatly thickened cell- walls of the epidermal cells, on 
which the mauvine does not seem to exert any influence. The 
cuticle is well marked as a bright purple external layer, contrasting 
strongly with the colourless thickened cells on which it rests. 
If any reliance is to be placed in the results obtained by stain- 
ing specimens with mauvine, there is one very important point I 
wish to mention. Schacht * states that the so-called intercellular 
substance, joining the walls of contiguous cells together, forms on 
the free surface of the cells what is known as the cuticle. By 
some the existence of this intercellular substance is denied ; and by 
careful examination of many specimens now before me, I can find 
no trace of any such material. The cuticle is brightly coloured, 
and if the same material existed as intercellular substance between 
the cells, a coloured layer should be seen between each of these cells, 
but none can be seen. If, then, the test of colour can be relied on, 
either intercellular substance does not exist, or else its composition 
is essentially different from that of cuticle. 
2. Staining with Beales Carmine Solution. 
When small portions of vegetable tissue are soaked in the car- 
mine solution, only those cells containing protoplasm appear stained. 
The nuclei and the granules in the protoplasm seem alone to be 
affected. The depth of colouring depends, then, on the number of 
granules in the protoplasm and the size of the nucleus. 
A. Experiments in Phalaris canariensis. — The rootlets of ger- 
minating seedlings of Phalaris canariensis were placed in a solution 
of carmine. When examined about twelve hours afterwards, the 
extremities of the rootlets were found to be very deeply coloured, 
while a faint tinge was visible along the other parts of the rootlet. 
Under the microscope the structure of the growing point of the root 
was beautifully seen. First a series of loose cells are seen at the 
extremity, continuing a short distance above the growing point. 
A very few of the most internal cells seem to be slightly coloured, 
the external ones being quite colourless. This mass of cells forms 
a regular sheath-like cap to the growing part of the root, very 
similar to the highly developed pileorhiza of Lemna. A well- 
* ' Grund. der Anat. imd Pliys. der Ge\vach.sc.' p. 29. 
