20 Botanical Microtechnique 



to produce slides showinti; mitochondria adecjuately for teaching pur- 

 poses, using Zirkle's modification of ErHki's fluid. 



Water 400 cc. 



Potassium bichromate 2.5 g. 



Ammonium bichromate 2.5 g. 



Cupric sulphate 2.0 g. 



Fix for 24 to 48 hr., wash in water, dehydrate and embed in paraffin. 



The desirability of wetting agents and penetrants in microtech- 

 nic]ue has been apparent to experienced workers for many years. 1 he 

 rapid development of numerous wetting agents in recent years has 

 led to considerable experimentation, with the expected diverse results. 

 The most prominent unfavorable effect of wetting agents are the 

 peeling of cuticle and epidermis, and varying degrees of cell distor- 

 tion. Further experimentation with the increasing number of a\ail- 

 able substances is certainly desirable. 



The wetting action of a substance can be tested easily. Make a 

 series of solutions of the substance to be tested by diluting a 1:1000 

 stock solution. Cut uniform pieces of a highly pubescent leaf and 

 drop alternating pieces into distilled water and into the dilutions of 

 the wetting agent. Note the relative time required lor the leaf pieces 

 to sink, and use the most dilute wetting agent that will sink the 

 tissues after brief aspirating. Determine whether the wetting agent 

 forms a precipitate or cloudiness with the killing fluid. If a reaction 

 occurs, do not add the wetting agent to the fixing fluid, but sink 

 the tissues in the wetting agent, rinse with water and (()\er with 

 the killing fluid. The final criterion is the condition of the tissues 

 in the finished slide, compared \\ith tissues processed without the 

 wetting agent. 



A workable terminology for designating killing lluid rorniulas is 

 a great convenience for giving oral or written instructions, or making 

 routine rccoicls. The name of the investigator who first devised a type 

 of formula is not always a satisfactory designation because the pro- 

 portions of the ingredients are necessarily \aried h)r (.liflerent subjects. 

 An arbitrary number is not sufliciently des(ripti\ f, excejjt among a 

 group of closely associated workers. Ihc ici minology pioposed here is 

 a compromise, the t\|)e ol loi inula is inclicatcd 1)\ a name or abbievia- 

 lion, and the |)i()p()rti()n ol ingredients 1)\ a ])(. i c cntage liguic. The 

 proportion of a solid like chromic acid is gi\en as piecentage by 

 weight; licpiicls like nulled glacial acetic acid aic gixcn as percentage 

 by volume. For instance, the time-honored chrome-acetic has numer- 

 ous \aiiants. one ol which is i'.-.\ ()..5-().r). meaning 0..5'; chromic acid 



