158 PREPARATION AND MOUNTING OF DOUBLE STAININGS. 



media which one may have occasion to use in mounting. Besides, 

 the cell is always soft enough to have the thin glass cover pressed 

 into perfect contact with it all around, which is the great requis- 

 ite in all fluid mountings. It should afterward be finished on 

 the outside with Brunswick black or shellac cement to form a 

 firm support to the thin glass cover. 



REPLY TO THE QUESTIONS RAISED IN THE DISCUSSION 

 'OF THE PAPER. 



In answer to the objections which have been made to the use 

 of chlorinated soda, on the ground that it is liable to destroy 

 the structure of tender vegetable substances, I w T ould say that if 

 leaves are dried and pressed, or stems are first dried and then 

 soaked before cutting into sections, they will not be injuriously 

 affected by the soda solution. At least that has been my experi- 

 ence. I am informed however that there are preperations sold 

 under the name of chlorinated soda, which are imperfectly sat- 

 urated with chlorine ; and consequently are still strongly alkaline. 

 These would naturally have the effect to destroy organic struc- 

 tures. Moreover, if this solution is exposed much to the light 

 there is a precipitate formed and deposited, which may leave the 

 fluid more strongly alkaline and therefore more destructive in 

 its effects upon vegetable tissues. The preparation known as 

 Labarraque's fluid, imported from France, is perhaps the most 

 reliable for bleaching purposes, though somewhat more expensive 

 than the home-made chlorinated soda solution. 



In regard to decolorizing vegetable substances by soaking in 

 alcohol, this may be very well with thin and tender specimens, 

 and where the object is to exhibit the cell contents ; but where 

 the object is to show the cellular structure or the fibro-vascular 

 tissues, I think that the results will be more satisfactory in the 

 use of the stronger chlorinated solution, which removes entirely 

 the cell contents, and makes the specimen more transparent, and 

 in my view far more beautiful. 



