322 BOTANJ. 



promycelium branches less frequently, and generally pro- 

 duces from three to four sporidia. In no other case than 

 Tilletia caries is the mode of entrance of the fungus into 

 the host plant known. 



415. No sexual organs have yet been discovered. They 

 are probably to be looked for just preceding the formation 

 of the spore-bearing hyphae. The uniting of the hypha- 

 branches in the germination of the spores of Tilletia cari*.'.-- 

 (Fig. 224, h) has probably no sexual significance. 



(a) In the study of the mycelium of the Ustilaginese, the hyphae 

 may be made more distinct in thin sections of the host plant by the 

 application of a solution of potassic hydrate. A similar effect is pro- 

 duced by treating the specimen for some hours with thinned glycerine. 



(b) In the study of the spore development, the specimens must be 

 examined in very early stages of the growth of the fungus. This can 

 generally be done in the case of those species which affect the Gram- 

 ineae, by taking the affected " suckers " or lateral branches of the host 

 plant, after the spores are pretty well advanced on the main stem. 



(c) Upon the application of a solution of iodine, the contents of the 

 young spores become yellow, indicating their protoplasmic nature ; 

 treated with Schultz's solution, the contents become brownish yellow. 

 The gelatinous membrane is not colored by the last-named reagent, 

 showing that it is not cellulose ; but when treated with a solution of 

 potassic hydrate, it is colored yellow, and in sulphuric acid it is dis- 

 solved. 



(d) The ripe spores frequently require to be treated with reagents to 

 bring out their structure. The endospore may be rendered visible by 

 the application of sulphuric acid which makes the epispore more 

 transparent ; in concentrated sulphuric acid the structure of the epi- 

 spore is made much plainer; treatment with a solution of potassic 

 hydrate causes the spore to swell up. 



(e) In the study of the germination of the spores, it is only neces- 

 sary to place freshly gathered spores in a drop of water, or upon 

 moistened earth, or in an atmosphere kept moist, as under a bell-jar. 

 Germination takes place in the proper temperature (20 to 25 C.,or 68 

 to 77 Fahr.) in from three hours (UstUago longissima) to fifty or sixty 

 (Tilletia caries). 



(/) All attempts thus far to determine experimentally the mode of 

 entrance of the fungus into the tissues of the host plant have failed, 

 with the exception of Kuhn's experiments upon Tilletia caries. The 

 recent attempts made by Fischer von Waldheim upon Ustilago carbo 

 and other species, although made seemingly under the most favorable 

 conditions, utterly failed. He placed fresh spores upon the germinated 

 seeds of oats and barley, upon the entire surface of the rootlets, and 



