Apr. 24, 1916 Watermelon Stem-End Rot 151 



signs of decay, while the 8 checks remained perfectly sound through- 

 out the course of the experiment. There was no decay present on 

 the inoculated melons except that which originated at the point of 

 inoculation. 



The decay is first noticeable as a somewhat circular discolored area 

 surrounding and extending from the point of inoculation. On the 

 watermelons observed in the laboratory this area gradually increased in 

 size until at the end of six days about half of the melon was involved. 

 At this time the advance of the decay seemed to become less rapid and 

 the area which was first decayed began to show a blackening due to the 

 formation of pycnidia by the fruiting fungus. This area spread daily, 

 and at the close of nine days the stem end of the melon presented a 

 withered, charred appearance. Plate XVII, figure i , is a reproduction of a 

 photograph of nine of these melons. The four in the upper row are 

 checks; the five below were inoculated. 



The fructification of the fungus may be briefly described as follows: 



Pycnidia separate or confluent, smooth or, under moist conditions, 

 covered with loose olivaceous hyphae, 180 to 250^1 in diameter. Spores 

 24 to 2>on by 10 to 14/X, oval, uniseptate, dark brown. On the material 

 taken from the watermelons inoculated in Washington no paraphyses 

 could be detected. They are present, however, when the organism is 

 grown upon potato cylinders, a fact which would tend to support the 

 conclusions reached by Taubenhaus,^ to whose work reference will be 

 made in the following paragraph. 



It has long been known that those members of the Sphaeropsideae 

 which produce brown uniseptate spores are extremely variable. The 

 distinctions between the genera Diplodia, Botryodiplodia, Chaetodiplodia, 

 Lasiodiplodia, and Diplodiella have been based on slight structural vari- 

 ations in the pycnidia. The points of separation are the relation of the 

 pycnidia to one another, whether scattered or cespitose; their relation to 

 the host, whether subcutaneous, erumpent, or superficial; the presence 

 or absence of bristles and of paraphyses. These are all characteristics 

 which one might expect to vary somewhat with the characteristics or the 

 condition of the host. This variation probably occurs; and for this rea- 

 son there has been some uncertainty as to the proper position certain 

 species should occupy in classification. Botryodiplodia theobromae Pat., 

 which causes a dieback of Hevea braziliensis in Ceylon, southern India, 

 and the Malay States, is an example; and in his account of this fungus 

 Petch ^ remarks that — 



Among the names which are known to refer to this species are Macrophoma vestita, 

 Diplodia cacaoicola, Lasiodiplodia theobromae, Diplodia rapax, and there are probably 

 others. Botryodiplodia theobromae is its earliest name, as far as is known, but some 

 prefer to call it Lasiodiplodia theobromae. 



* Taubeahaus, J. J. The probable non-validity of the genera Botryodiplodia, Diplodiella, Chaetodip- 

 lodia, and Lasiodiplodia. In Amer. Jour. Bot., v. 2, no. 7, p. 324-331, pi. 12-14. iQiS- 

 'Fetch, Thomas. Physiology & Diseases of Hevea braziliensis . . . 268 p., 16 pi. Loudon, 19x1. 



