226 AGBICULTURAL EXPERIMENT STATION. [Jan. 



at least, is one of the most common and widely spread mem- 

 bers of the group Erysiphe Oichoraceariim. The winter 

 stage consists of tiny, dark-brown, rounded capsules, con- 

 sisting of a lirm outer crust of compacted cells, enclosing a 

 group of spore sacs. Within these sacs, when mature, are 

 formed the spores. The structure of the perithecia, asci, 

 spores and haustoria of the cucuml)er fungus identifies it 

 beyond doubt as the species above named. I have not been 

 able to duplicate the lost drawings of a perithecium, Init fig. 



18 shows a group of characteristic asci with spores, and fig. 



19 a single ripe spore. These spores undoubtedly carry the 

 fungus over from season to season, but nothing is yet known 

 as to their germination and further development. 



3. The Downy Mildew. — Plasmopara Cubensis (B. & C.) Humph 

 In a previous report of this station* will be found an 

 account, with figures, of this downy mildew of cucurbita- 

 ceous plants, which, though but recently recognized in this 

 country, has come to be a serious pest. So far as I know, 

 its occurrence on the cucumber plant in the greenhouse has 

 not heretofore been mentioned, though it has often been 

 observed in the open air and in the hot-bed. This fungus 

 was received about October 1, in large quantity, on leaves 

 of greenhouse cucumbers, from Messrs. C. H. Chase & Son 

 of Clinton, who report that they have suffered from its 

 attacks for two years previous to the present. On leaves 

 attacked by this fungus, it is not commonly sufficiently 

 abundant to be recognized by the unaided eye, as the spore 

 threads are rather thinly scattered over the lower faces of 

 the leaves. But on the material above mentioned the 

 development of the fungus was very luxuriant, perhaps 

 fnrni the peculiarly favorable conditions afforded by the 

 greenhouse. The lower leaf surfaces showed the distinctly 

 purplish tint, due to the abundant development of summer 

 spores, which characterizes the presence of various nearly 

 related fungi on other hosts. These individuals presented 

 no differences in structure from those developed out of doors, 

 but the difference in luxuriance of develo})nient was very 

 striking. 



* Eighth Report Massachusetts Experiment Station, p. 210, and PI. II. 



