204 



Methods in Plant Histology 



are abundant and are very easy to fix and cut. The infected plants 

 are also very easily recognized, normal plants having the prostrate 

 habit, while infected plants become erect and the internodes become 

 greatly elongated. Aecidia growing on Arisaema triphyllum (Jack- 

 in-the-pulpit) are also easy to cut. The Aecidium on Hepatica 



has large nuclei and affords particularly 

 good views of the intercalary cells 

 (Fig. 58). 



Flemming's weaker solution is recom- 

 mended for fixing and iron-haematoxylin 

 with a faint touch of orange is a satis- 

 factory stain. 



It is rather difficult to get good sec- 

 tions of uredospores and teleutospores of 

 Puccinia graminis, because the leaves of 

 wheat and oats are refractory objects to 

 cut. For illustrative purposes, soak the 

 leaves, scrape off the spores, and study 

 without sectioning. For sections, select 

 species growing on less refractory hosts. 



Everyone who studies the rusts should 

 attempt to germinate the uredospores and 

 teleutospores. For this purpose the 

 hanging-drop culture may be employed, 

 as described in the chapter on temporary 

 mounts (chap. v). The uredospores ger- 

 minate readily all summer, but in most 

 forms teleutospores will germinate only 

 in the spring following their maturity. 

 However, the teleutospores of "lepto" species, like Puccinia xanthii on 

 Xanthium canadense (cockle-bur), will germinate as soon as they 

 ripen, and will serve equally well for study. If a particularly good 

 specimen is secured, it may be preserved by the method previ- 

 ously described for desmids, except that in this case it might be 

 worth while to attempt staining with Mayer's haem-alum, or with 

 eosin. 



FIG. 58. Aecidium on He- 

 patica: fixed in chromo-acetic 

 acid with a little osmic acid, and 

 stained in safranin, gentian- 

 violet, orange; from a prepara- 

 tion by Dr. Wanda M. Pfeiffer. 

 X950. 



