The Grape Rot. 225 



beetle, but it was subsequently shown to be that of a chalcid fly (Isosoma vitix, 

 Saund.). The maggot feeds in the seeds of the grape, one or two of which 

 enlarge considerably as a result of its attack. 



Last fall, on the invitation of Mr. A. L. Hatch, of Ithaca, Wis., I spent sev- 

 aral days at his home in the examination of rotting grapes. The greater 

 ninnber of the diseased berries in his vicinity were simply drying up and 

 falling, with no external sign of insect attacks. These berries, when cut open, 

 showed quite uniformly a discolored appearance before any trace of injury 

 could be seen at the surface. As a rule, while most of the pulp remained un- 

 affected, a zone of browned tissue could be seen running almost or quite 

 aronnd the fruit between the seeds and the skin. In sections of this diseased 

 tissue I was able to make out the presence of a fungous mycelium, which is 

 evidently that of some Peronospora, and possesses the small, round haustoria 

 or suckers of the mycelium, which is found in grape leaves attacked by the 

 American grape mildew (Peronospora viticola, B. &, C). Sections of grapes 

 containing this mycelium were placed in damp air, and in the course of a few 

 days several of them produced a small quantity of the fruit characteristic of 

 this Peronospora. 



It appears, therefore, that the most destructive form of the grape rot with 

 us is a direct result of the growth in the berries, of the fungus which causes 

 the common leaf disease of the vine. This fungus forming, when in fruit, 

 frosty white patches on the under surface of the leaves, which are browned 

 above in corresponding places, should be familiar to every grape grower; 

 but it is. unfortunately, the case that many horticulturists do not distinguish 

 it from the Oidlum or true mildew of their upper surface. 



Heretofore this Perunospora has been found only on the vine, fruiting 

 abundantly on the leaves, sometimes on the shoots of the plant, and rarely 

 on the fruit the epidermis of which, perforated by no stemata or breathing 

 pores, usually prevents the emergence of its fruit-bearing threads. During 

 the past season it has also been found on a near relative of the grape, the 

 Virginia creeper (Ampdopsis qainqwfolia), in several parts of the West, e. g., 

 in Minnesota by Prof. Farlow, and in two localities in Wisconsin by myself 

 and Mr. L. H. Pammel, one of my students. 



From what has been said, it will be seen that what is generally known as 

 " the gnipe rot " is not one disease, but that this is a generic name, including 

 several well marked disorders. For convenience I append a key that will 

 probably enable any careful observer to determine the cause of either of 

 these, or if there are still others, to determine that fact: 



1. Insects not found in the pulp, 2. 

 Insects found in the pulp, 4. 



2. Minute black dots on a dried gray spot, Phi»ii% uvicola (B. it C). 

 Berries shriveling, not appearing scorched, 3. 



3. Berry not punctured, seels not enlarged, Peronospjri vUiculv (13. it C). 

 Berry punctured or discolored at one spot, one or two seeds enlarged, 



containing a footless maggot, Isosomi vitis (Saund.). 



