292 SalmOD, On Specialization of Parasitism in the Erysiphaceae. 



20 days the perithecia were examined, and in the 50 opened the 

 asci showed no signs of developing ascospores. 



In another experiment a small piece of a leaf bearing peri- 

 thecia was placed, after being just moistened, on a small damp 

 piece of filter-paper at the bottom of a glass tube. The air-pump 

 was then applied to the tube for 4 hours, when the tube was 

 hermetically sealed. After 18 days the perithecia were examined, 

 and were found to possess asci which almost without exception 

 contained ascospores. These latter were 4 or 8 in number, and 

 were apparently quite ripe, being usually found free in the peri- 

 thecium. The leaf on being taken out ofthe tube was still slightly 

 damp. The experiment shows that a very small amount of moisture 

 is suificient to enable the fungus to produce ascospores. 



Bibliography. 



1. Salm OD, E. S.; A monograph of the Erysiphaceae. (Mem. Torrey Bot. 



Club, IX. [U)00]). 



2. Idem; Supplementary Notes on the Erysiphaceae. (Bull. Torrey Bot. 



Club, XXiX, 1-22, 83-109, 181—210, 302—316, PL 9—11 (1902). 



3. Idem; On the Increase in Europe of the American Gooseberry-mildew. 



(Journ. Roy. Hort. Soc. [London], XXVIJ, 599 [1902]j. 



4. Neger, F. W. ; Beiträge zur Biologie der Erysipheen. (Flora, XC, 



221—272, Jan. 1902). 



5. Schrenk, H. von.; On the Teaching of Vegetable Pathology. (Bull. 



Torrey Bot. Club. XX IX, (32, (33 [1902]). 



6. Marchai, E. ; De la specialisation du parasitisme chez VErysiphe graminis. 



(Comptes Rendus, CXXXV, 210—212, [July 21, 1902]). 



7. Dangeard, P. A.; Second Memoire sur la Reproduction sexuelle des 



Ascomycetes. (Le Botaniste, V, 2(32, fig. 5, [July 1897]). 



8. Ward. H. Marshall; On the Relations between Host and Parasite in 



the Bromes and their Brown Rust Puccinia dispersa Erikss. (Annais 

 of Botany, XVI, 233—315 [June, 1902J). 



9. Klebahn, H. ; Kulturversache mit heteröcischen Rostpilzen. (Zeitschr. 



für Pflanzen krankh.. Vi, 262 [1896J). 

 10. Wolff, R ; Beitr. zur Kenntn. der Schmarotzerpilze {Erysiphe graminis 

 und E. communis [1875]). 



Explanation of Plate. 



Fig. 1. Conidiophore , with chain of nearly ripe conidia, of the Oidium of 

 Erysij^hc Graminis DC. on Bromus inferruptus X 255. 



Fig. 2. Portion of the mycelium of the same fungus, showing the young 

 stages in the development of the conidiophore X 400. 



Fig. 3. Ripe conidia of the same; the lowest two examples of the abnormally 

 large conidia which occasionally occur X 400. 



Fig. 4 — 7. Germinating conidia of the Oidium on £. interruptus, üoating on 

 the surface of water; 4, after 48 hours, showing the long germinal 

 tube rising vertically into the air X 255; 5, the same, in an earher 

 stage, X 400; 6, another conidium, germinating after 48 hours, X 255; 

 7, the same, X 400 



Fig. 8, 9. Contiguous conidia of the Oidium of E. Graminis on Triticum 

 vulgare, germinating on the surface of water, 5 days affer sowing 

 X '255. 



