754 Botanical Microtechnique 



selected pieces of the culture agar and kUlin^ in FAA, which also 

 serves as a storage fluid. Such material can be used for mounts in water 

 or lactophenol or for excellent stained permanent preparations of 

 whole mounts (Chap. 10) . Cytological preparations reqture such 

 highly specialized and almost specific methods that the ambitious 

 student shoidd study the research jiublications of a given species for 

 details of procedine. 



Odtnycetes.—PlasinodiojjIioKi brdssicae is parasitic in the roots of 

 cabbage and related plants. The plasmodium can be demonstrated in 

 young roots that are just beginning to undergo distortion. Stages of 

 cleavage and spore formation are obtained from increasingly gnarled 

 and distorted roots. FAA gives good fixation, but Craf III is superior. 

 A simple hemahmi-safranin stain is adequate for most purposes, 

 safranin-fast green is more contrasty, and iron hematoxylin gives the 

 most brilliant differentiation of the parasite nuclei. 



Syncliytriiim decipiens, parasitic on the hog peanut, and related 

 jiarasites yield striking preparations, but poor fixation is frequent, 

 and sectioning is improductive, making the slides somewhat expen- 

 sive. Craf II was found to give excellent fixation. Iron hematox)lni is 

 by far the most satisfactory stain. 



Saprolegnia and allied water molds are readily obtained and easily 

 cultured, furnishing abundant vegetative and sexual material for 

 stud\ in tire living condition. The best soinces are dead fish and Avatcr 

 insects, or steam sterilized house flies placed into a large crock of 

 pond water. Whole mounts can be piepared h\ the general methods 

 given for filamentous plants (Chap. 10) . Ascertain the correct killing 

 formula lor the species being studied by testing small masses in a 

 weak chrome-acetic or Craf I and manijiulating the acetic (or 

 jji()j)ionic) acid (ontent. W'hole-niount and sectioning methods are 

 used for cytological study, and the reader is referred to research 

 publications for these highly specialized and dilficult methods. 



Pythium and Pliytoplitliora are most effectively studied in 

 culture, 1)111 preparations (an l)e made by the methods suggested for 

 the water molds. 



Albugo (Cyslopiis) . the "white rust," is an indispensable subject 

 in teaching. Several species octm on (onunon crops and \\eeds. For 

 the conidial (zoosj)orangial) stage, select jnistides that ha\e just 

 ruptured. Fully openetl pustules Avill have most of the spores washed 

 out dining processing. Fhe sexual stages arise after the conidial stage 

 is on the decline, and the host tissues show evidence of hypertrophy. 

 A. Candida and A. hliti are fixed in perfect condition in Craf II. 



