308 W. H. GILBURT ON THE STAINING OF VEGETABLE TISSUES. 



medullary sheath is tinted with the colour, and eventually, when the 

 pith practically becomes inactive, it is neutral, refusing all colour, 

 or taking both. 



These facts stand good in all cases, whether the section is bleached 

 in alcohol or in the soda solution, or stained when fresh cut, without 

 any preparation whatever. Neither does it matter how the colours 

 are presented, whether magenta first, or the reverse, by single or 

 alternate immersion. 



In preparing leaves for staining, the bleaching process must be 

 carried farther than with sections ; as before stated, not only must 

 the colour be discharged, but all the cell-contents removed ; there- 

 fore they must be left in the soda solution till quite translucent. 

 The time occupied in the process varies according to the texture of 

 the leaf, from a few hours to a week or more. When very delicate 

 leaves are to be bleached, it will be well to dilute the bleaching fluid 

 with one third its bulk of water, otherwise disintegration may set in 

 before the process is complete. Leaves, if large, should be cut into 

 pieces, rather larger than required for mounting. 



The process for washing is just the same as that given for sec- 

 tions ; after which they must be placed in alcohol. 



In staining leaves the question naturally arises, which of the two 

 colours given is the best to use ? The answer must entirely depend 

 upon the purpose for which the preparation is required. If it is 

 desired to exhibit the structure of the lamina, then blue should be 

 used, because, if the colour be good, it marks out the cell-walls far 

 more distinctly than magenta ; and, moreover, the latter colour, if 

 occupying the whole field of the microscope, would be most injurious 

 to the sight, if worked with for long. There is also the difficulty 

 of fixing magenta, unless it is passed through benzole instead of oil 

 of cloves. This of course may be done, but it always produces a 

 more or less injurious effect upon the tissue. 



In using the blue dye, no definite time can be given for immer- 

 sion, it altogether depending upon the density or permeability of the 

 tissue. Dr. Beatty recommends that two solutions should be pre- 

 pared — a quarter and a half-grain solution, and that the leaf should 

 be transferred to the stronger if not stained sufficiently in the weaker 

 one in half-an-hour. To this, however, there is the objection, that 

 sometimes far too much colour will be taken up in parts, which must 

 then be washed out, leaving generally a very mottled appearance, 

 while, if the solution I have used be adopted, the object may remain 



