136 REPORT OF THE COMMISSIONER OF AGRICULTURE. 



EXPLANATION TO PLATE I. 



THE DOWNY MILDEW OF THE GRAPE, CONIDIA, CONIDIOPHORES, ETC. 



Fia. 1. A conidium, or "summer spore." 



Fig. 2. A similar conidium, in which tlie contents has commenced segmentation or 



division into zoospores. 

 Fig. 3. A similar spore, representing a more advanced stage in the segmentation. 

 Fig. 4. Zoospores escaping from the conidium. 

 Fig. 5, A zoospore more highly magnified, showing the two cilia. 

 Fig. 6. Same as Fig. 5, having lost its ciha and assumed a definite shape. 

 Figs. 7 and H. The same, pushing out germ tube. 



Fig. '9. The shaded portion reprensets a fragment of mycelium of the Mildew grow- 

 ing between the cells of the host plant, a, a, suckers or haustoria (after 

 Farlow). 

 Fig. 10. A groui> of fructiferous filaments or conidiophores, which have grown out 



of the leaf through one of the "breathing pores" (after Cornu). 

 Fig. 11. Fecundation of the oospore from a sample found in the tissue of a mildewed 



leaf, a, the antheridium when about to emit its protoplasm into the 



oogonium (after Viala). 

 Fig. 13. An oospore, or "winter spore" (after Cornu). 



EXPLANATION TO PLATE II. 



CONIDIA, ASCUS-FRUIT, ETC., OF UNCINULA SPIRALIS, B. AND C. 



Fig. 1. Mycelium from surface of grape leaf, showing two haustoria and three up- 

 right conidiophores in different stages of gi-owth. At the right above are 

 two mature conidia, one of which is rej)resented as just detached from its 

 supi^ort. 



Fig. 3. A germinating conidium, or summer spore. Tlie spore may give rise to one 

 or several germ tubes. These spores serve for the propagation of the fun- 

 gus tlu'ough the summer and autumn. 



Fig. 3. Epidermis of grape-berry upon which the mycehum of Uncinula has gi-own. 

 Much enlarged; to the unaided eye the effects of the mycelium on the 

 berry are visible as brown lines, dots, or blotches. 



Fig. 4. Perithecium, or ascus-fruit, showing pseudoparenchymatous structure; the 

 coiled arms, or appendages; and three escaping asci with the inclosed 

 spores — winter spores, thecaospores, or ascospores, as they are variously 

 called. The normal number of spores is six. The conidia occur tlu-ougli« 

 out the season ; the perithecia are formed in autumn. 



EXPLANATION TO PLATE III. 



VARIOUS STAGES IN THE DEVELOPMENT OF PHYSALOSPORA BIDWELLII, SACC. 



Fig. 1. A fragment of epidermis of a diseased berry, showing five of the black pus- 

 tules formed by the development of the pycnidia. From four of these, 

 slender, contorted, worm-like filaments are being extruded; these are the 

 stylospores held together by a kind of mucilage. 



Fig. 2. A section through a bit of the berry, including an immature pycnidium (P) 

 and sijermagonium (S). At O is the osteolum of the pycnidium, through 

 Avhich the spores escape at naaturity. m m are dark-brown, septate my- 

 celial threads from the conceptacles. 



Fig. 3. A section of a portion of a pycnidium, more highly magnified, showing the 

 basidia, or the stalks upon which the stylospores are borne, and several 

 detached spores. 



Fig. 4. Section through the exterior portion of a pycnidium, showing conidiophores 

 and conidia growing from the surface. 



Fig. 5. Three stylospores germinating. 



Fig. 6. A section through the perithecium or conceptacle of the ascosporous form, 

 showing the asci, &c. 



Fig. 7. Two separate asci, showing the eight sporidia in each. 



Fig. 8. An ascus, inclosing eight sporidia, found June 2, 1886, in grape (destroyed 

 in 1885 by Black-Rot) kept for a week in moist air. Fi-om camera-lucida 

 sketch made by Erwin F. Smith in the laboratory of the University of 

 Michigan. Mr. Smith notes that the "receptacles contaLaing the asci are 

 numerous, and the asci themselves abundant." 



Fig. 9. Four of the sporidia that have escaped from an ascus. 



