94 The Plant World. 



solution of chloral hydrate, where they may remain until wanted 

 for study, or for further treatment. 



If the material clears with difficulty, the process may be 

 hastened, by first treating the specimens for t went v-f our hours 

 or over night, in a ten per cent aqueous solution of hydrocloric 

 acid, and then proceeding in the usual way. The whole process 

 of clearing may be further facilitated, by keeping the reagents 

 containing the specimens upon the paraffine oven, or in some 

 other warm place. 



It is sometimes advisable to treat the specimens with a weak 

 solution of acetic acid when they are removed from the potassium 

 hydrate, in order to remove all traces of this reagent. A thorough 

 washing in water, however, will render the acid bath unnecessary. 



The length of time for treating leaves with chloral hydrate, 

 may be determined by an occasional examination of them. As 

 soon as they are colorless or transparent, they must be passed 

 to the potassium hydrate. Some material, however, would 

 never become colorless with any treatment with chloral hydrate. 

 Leaves of desert plants have been boiled and incubated for 

 months in chloral hydrate, with the result that they seemed 

 more deeply colored than they were at the beginning. 



The length of time for treating leaves and stems with potas- 

 sium hydrate, may be governed by examining them ocaasi^ially 

 with the microscope. , Twenty-four hours are ample for many 

 of the ordinary specimens. 



Leaves and stems cleared in this manner, show their cell 

 wall structure better than when treated in any other way. Bits 

 of leaves and sections of stems so prepared are very satisfactorily 

 studied without staining, when temporarily mounted in concen- 

 trated chloral hydrate or dilute glycerine. 



It is desirable, however, to stain them by the f illowing meth- 

 od : Prepare a deep red stain by dissolving saf ranin in a satur- 

 ated aqueous solution of chloral hydrate; stain the whole leaves 

 or parts of leaves in this for a few hours or over night; rinse in 

 water, bleach in concentrated chloral hydrate for a few moments, 

 or until the stain is removed from all of the tissues except the 

 tracheal elements of the veins; wash in water and transfer to 

 dilute glycerine, where the specimens may remain indefinitely, 

 or be mounted in glycerine jelly. Whole leaves treated in this 



