20 METHODS IN PLANT HISTOLOGY 



is long enough. Root-tips of the onion, anthers of the hly, and similar 

 objects require from 15 to 30 minutes. Larger objects may require an 

 hour. No washing is necessary, but all plant tissues contain water; 

 consequently, if material is to be imbedded in paraffin, the alcohol used 

 for fixing should be poured off and fresh alcohol added before proceed- 

 ing with the clearing. If material is to be mounted in Venetian turpen- 

 tine, as is hkely to be the case in small filamentous fungi, the transfer 

 to the stain may be made directly from the absolute alcohol to any 

 stain dissolved in an alcohol not weaker than 85 per cent. Small forms 

 with no vacuoles may be transferred to a weaker alcoholic stain or even 

 to an aqueous stain ; but neither the fixing nor the rude transfer would 

 be at all satisfactory with forms like Zijgnema or Saprolegnia. 



Acetic acid is used with alcohols to counteract the tendency to 

 shrink. One of the most widely known of the alcohol combinations is 



c) Carney's fluid. — 



Absolute alcohol 6 parts 



Chloroform 3 parts 



Glacial acetic acid 1 part 



The penetration is very rapid. An object like an onion root-tip is 

 doubtless killed in less than a minute and 15 or 20 minutes is long 

 enough to fix an object of this size. Wash in absolute alcohol, changing 

 frequently, until no odor of acetic acid or chloroform remains. For a 

 root-tip, the entire process does not require more than an hour. It 

 is better to imbed in paraffin at once, but when this is not convenient, 

 the material may be washed in absolute alcohol until the odor of acetic 

 acid and chloroform disappears, cleared in xylol, and, with a block of 

 paraffin about half the bulk of the liquid added, may be left indefinite- 

 ly. Cyanin and erythrosin, fuchsin and iodine green, and similar com- 

 binations stain brilliantly after this reagent. 



d) Acetic alcohol. — Farmer and Shove recommend for fixing root- 

 tips of Tradescantia virginica a mixture of 2 parts absolute alcohol and 

 1 part glacial acetic acid. The mixture is allowed to act for 15-20 

 minutes, after which the acid is washed out with absolute alcohol and 

 the material is imbedded as soon as possible. 



e) Formalin alcohol. — This is one of the most satisfactory alcohol 

 combinations. Various proportions are used by different workers. 

 Professor Lynds Jones, who first brought the combination to my no- 

 tice, added 2 c.c. of commercial formalin to 100 c.c. of 70 per cent al- 



