282 Pflanzenkrankheiten. 



a species of fruit fly which lay their eggs in the rotting potato, the 

 longevity of the Rhisopus mycelium in the affected host, all these 

 are described with many details, a great deal of which are new. 



About ring rot, the Symptoms of which are als described, the 

 author has made a great many of proofs that ring rot and soft rot 

 are both caused by the fungus Rhisopus nigricans Ehr. and not by 

 Nectria ipomoeae as Halsted believed. The more important conclu- 

 sions reached are these: 



Ring rot, like soft rot, Starts early when the sweet potatoes 

 are first brought into storage. In fresh rot, as in fresh soft rot, the 

 fungus does all the damage in a very short time. usually within 

 twenty-four to forty-eight hours. The infected parts in both rots are 

 very soft and water-soaked. In both, the water may leak out through 

 some break in the epidermis. the tissue drying in proportion as the 

 water is lost. Like soft rot, ring rot, under storage conditions, does 

 not send out sporophores unless a break occurs on the epidermis 

 and this usually happens through the weight and pressure of the 

 surrounding rots. In this case the sporophores are short, very 

 numerous, closely packed, and borne at the break in the epidermis. 

 As in soft rot, when roots freshly infected with ring rot are placed 

 in a moist chomber, the fungus R. nigricans grows out at the area 

 of the ring within twenty-four hours. In plating out tissues from 

 sweet potatoes freshl}'- infected with ring rot, a pure culture of the 

 Rhisopus fungus is obtained in from twelve to sixteen hours. Within 

 a week to ten days after infection, the diseased tissue of ring rot, 

 just äs in soft rot, is odorless, but is soon foUowed by termentation. 

 At this stage the causative organism begins to die. Ring-rotted sweet 

 potatoes, like soft rotted ones, after reaching an age of ten days to 

 three weeks, upon being placed in a moist Chamber, fail to develop 

 any Rhisopus-gYowih from the infected area. Platings made from 

 these roots fail to produce any Rhisopits- growth, but on the con- 

 trary produce fungi like Oospora laciis, Oosporoidea lactis and bac- 

 teria. Crush mounts of the tissue from old ringed areas under the 

 microscope reveal the presence of the Rhisopus fungus, the fila- 

 ments, however, being either empty or the protoplasm browned and 

 broken up into small granules, indicating the absence of life in 

 these hyphae. Last, ring rot can be produced by inoculating fresh 

 spores from a pure culture of R. nigricans Ehr. into punctures 

 made in health}^ but susceptible sweet potato roots placed in a 

 moist Chamber and kept from 70 to 80° F. The fungus can readily 

 be reisolated from the fresh soft ring, but if a week to ten days is 

 allowed to elapse after the formation of the artificial ring, an active 

 fermentation sets in and the causal fungus soon dies out. The for- 

 mation of the ring rot seems an accidental process where the fungus 

 strikes the susceptible area. Uneven ripening may also be a factor 

 in ring rot formation. 



The Symptoms and pathogenecit}" of vine wilt yellows (stem rot) 

 as caused by Fusarium batatatis VVoU. are also described in this 

 paoer. The results of the writer conclude with those of Harter and 

 Field (Phytopathology. IV. p. 279—304. vide Bot. Cbl. ßd. 129. p. 2551 



Last, the writer describes briefly a new Icaf spot, which attacks 

 the foliage in the field and is attribed to what appears to be a new 

 species of Septoria. named by the writer 5. bataticola Taub. nov. spec. 



M. J. Sirks (Haarlem). 



Tolksy, A., Die Gipfeldürre der Kiefer in Buzuluksky 



