158 Botanical Microtechnique 



can be detached from the substratum and processed easily, ^vliereas 

 the parasitic members require adequate preservation of both parasite 

 and host. In the following discussion the taxonomic order is sub- 

 ordinated to methods of preparing the material. 



Us tila ginnles .—These parasites occur on a wide range of hosts, but 

 the most interesting members occur on important crop plants. Ustilago 

 zeae, the corn smut, is found on all aerial parts of the corn plant. 

 Smut galls on stems, leaves, and ovaries should be collected. Very 

 young smut galls, that ha\e not markedly distorted the organ being 

 attacked, show the host cells in good condition, and contain acti\e 

 and rather sparse mycelium. Kill this stage in Craf III. Older galls 

 having a milky white interior contain a great mass of mycelium and 

 distorted host cells. Small pockets of chlamydospores occur in the 

 white mass. This stage, which can be ascertained by freehand sections, 

 is the latest useful stage. Kill these older galls in FA A. 



Ihe mycelium of corn smut has a strong affinity for hcmalum, ami 

 a simple hemalum-safranin stain shows the hyphae stained blue-black, 

 chlamydospores stained red, the thin walls of the host cells stained 

 blue, and the lignified elements stained red. Use iron hematoxylin for 

 nuclear studies. 



Other common smuts, such as Ustilago levis, U. Iiordei, U. m'cune, 

 and the bunts, like Tilletid Iritici, can be processed by the abo\e 

 methods. 



The chlamydospores of many smuts and bunts germinate readily 

 in water or carrot decoction. The promycelia and sjioridia are studied 

 best from wet mounts from cultiue, but the material c an be made into 

 permanent mounts by the dioxan or butyl alcohol methods (Chap. 

 10). 



Uredinales.— The rusts rank among the most destructive and wick- 

 spread ])lant pests, and class materials illustrating ilu' important 

 phases of the life cycle of the rusts are indispensable. The story of 

 wheat rtist has been so well publicized that the organism may well be 

 the standard item representing this groiq). 



Puccinia gxiininis has its red uredinial and black telial stages on 

 wheat and many other grasses, rhe red summer-spore stage occurs on 

 young leaves and is therefore easy to section. I'he black winter-sj)ore 

 l)usiules occur on older leaves and on the stems, both of which are 

 diliicuh to section without tearing. Use the youngest leaf showing the 

 telial stage, avoiding the use of stem material if possible. Kill in 1.1 A 

 and process like any leaf parasite. The pycnial (spermogonial) and 

 aecial stages on barberry occur on young, tender leaves that are 



