68 THE ELEMENTS OF VEGETABLE HISTOLOGY 



more apparent by the application of reagents and 

 stains. The color changes incidental to the action 

 of reagents are due to chemical interaction, whereas 

 with stains the coloration is usually due to a satur- 

 ation of the cellular material with the dye. It is noted 

 that certain tissues color easily with a given stain, 

 while others are indifferent to its action. Certain 

 stains may thus be used to differentiate cellular elements 

 and contents from others closely resembling them. 

 Stains used for this purpose are termed differential 

 stains in contradistinction to general stains, which 

 color most, if not all tissues The effects of differential 

 stains are somewhat analogous to the actions of re- 

 agents. Formulae for the staining fluids recommended 

 in the following notes will be found in the Ap- 

 pendix. 



Cellulose: 



Delafield's hematoxylin : 



Cellulose walls are colored violet. The time required is 

 five to fifteen minutes. 



Lignified Tissues'. 



Delafield's hematoxylin : 



Lignified walls are colored yellow to brown. The time 

 required is at least thirty minutes and generally longer, 

 depending upon the texture of the material. 



Fuchsin : 



Lignified walls are stained deep red. Aqueous solutions are 

 used and the time required is fifteen to thirty minutes. 

 Best results are obtained by washing the stained material 

 for five or ten minutes in Altman's picric acid solution. 



Cutinized and Suberized Tissues. 



Cutinized cell walls stain slowly and with difficulty. Cyanin, 

 saturated solution in 50 per cent alcohol, stains cutinized 

 membranes deep blue. The time required is at least twenty- 

 four hours. 



