348 Journal of Agricultural Research voi.xv, no. 6 



ally becoming mummified (PI. 25, A). The spores may be of three types 

 and sometimes all three may be found in the same pycnidium. In the 

 young pycnidium they are usually hyalin and i -celled, and occasionally 

 this is the only type found; but usually a little later the hyalin spores 

 turn dark, and may or may not be septate. In the old mummied potato 

 the 2-celled dark spores predominate, but are intermixed with a few 

 I -celled dark and a few i -celled hyalin spores. 



INOCUIvATlON EXPERIMENTS 



The first inoculation experiments were made on January 16, 1914, 

 when spores and hyphae were inserted into a wound at the end of eight 

 healthy roots, four with Diplodia tuhericola from dasheen and four with 

 the same organism from sweet potato. These potatoes were kept in an 

 uncovered vessel in the laboratory. This method was followed because 

 preliminary experiments showed that better results could be obtained 

 by exposing the inoculated roots to the dry conditions of the laboratory 

 room than in a moist chamber. Just why this should be has not been 

 determined. On February 18, six of the potatoes were partially rotted 

 and on March 12 all but two, which remained sound, were completely 

 decayed, D. tuhericola being recovered in pure culture from each. On 

 May 8, eight potatoes were inoculated with D. maclurae and placed in 

 an uncovered moist chamber. One of these potatoes remained sound, 

 but the others were completely decayed by July 11. 



On September 2, 1914, twelve sweet potatoes were inoculated with 

 Diplodia gossypina. Six were inclosed in a damp chamber with moist 

 filter paper in the bottom, and six were placed in an open receptacle. 

 On October 15, in the open vessel the results were as follows: Two were 

 completely rotted, two one-fifth rotted, and two sound. The fungus was 

 recovered from the four decayed potatoes. In the moist chamber one 

 was completely rotted, one one- third rotted, and four sound. From 

 one of the rotted potatoes D. gossypitia was isolated, and from the other 

 an unknown fungus. 



On January 5, 191 5, six sweet potatoes were inoculated with Diplodia 

 zeae (Schw.) Lev. All remained sound. 



On January 14, 191 5, ten sweet potatoes were inoculated with Diplodia 

 tuhericola from sweet potato. Five were immediately placed in aa 

 incubator (34°-35° C), and five in an ice box (i2.2°-i3.5° C). On 

 February 8 two potatoes in the incubator were entirely rotted, and one 

 remained sound. On February 23 one of the two remaining potatoes was 

 half decayed and the other entirely decayed. There was no e\ddence of 

 decay in the potatoes in the ice box on January 25, but by January 29 

 two had been completely rotted by Rhizopus nigricans. By March 31 

 two were partially rotted, and D. tuhericola v^^^s isolated in pure culture. 

 The remaining potato was completely decayed, and Alternaria sp. was 

 obtained in pure culture from it. The best results were obtained at the 

 higher temperature. 



