78 Journal of Agricultural Research \oi. v. no. 2 



and after having nourished several plants to partial maturity. Two days 

 later an examination showed that spores and conidiophores were develop- 

 ing on two of the tubers ; but no indication of infection was observed on 

 either the leaves or stems which were placed in a moist chamber. 

 Examination on the following day showed no further developments, and, 

 as the potato plants were becoming very much discolored, the observa- 

 tions were discontinued. It should be noted at this point that the fungus 

 was alive and able to sporulate on the diseased tubers after being in the 

 soil for 45 days at a temperature between 15° and 20° C. Had the fungus 

 been latent in the potato leaves and stems, as claimed by Massee (20), 

 it should have developed. The most interesting and important fact 

 brought out in this experiment was the production of healthy vines 

 by a tuber having in it the mycelium of P. infestans which remained alive 

 for 45 days. 



The two pots which were kept at 23° to 27° C, one containing three 

 infected tubers and the other three healthy tubers, came up a little earlier 

 than those kept at 15° to 20° C. The first shoot came up on February 4, 

 or 6 days after planting, and in 10 days all three of the diseased tubers 

 had shoots up, some of them longer than others. The development of 

 the tubers used as controls was several days behind that of the diseased 

 tubers. Ten days after planting, the shoots were so tall in the pot contain- 

 ing diseased tubers that the pane of glass had to be replaced by a bell jar. 

 The control was treated similarly. Nothing of special interest occurred 

 until March 8, or 39 days after the tubers had been planted, when it was 

 noticed that one of the small shoots growing from one of the diseased 

 tubers appeared water-logged at and a short distance above the surface 

 of the soil. It did not have the normal appearance common to the stems 

 of the other seven shoots in the pot. Upon examination of the water- 

 logged area with a hand lens, a white glistening growth could be seen on 

 the surface. Some of this material was carefully removed and exam- 

 ined microscopically and proved to be spores and conidiophores of P. 

 infestans. This infected plant was about 2 inches tall, spindly, Ught 

 green, and less robust in appearance than some of the other plants in 

 the same pot (PI. V). The soil was carefully dug away from the stem, 

 and a portion of it below the soil was found to be diseased. This portion 

 gradually became darker as it approached the mother tuber, being brown 

 and doubtless dead at the point of attachment. The parent tuber was 

 nearly all decayed, except one small portion, which was still firm and from 

 which the diseased shoot in question had developed. Free-hand sections 

 made of the portion of the parent tuber where the stem was attached 

 showed the presence of a nonseptate fungous mycelium which was un- 

 doubtedly that of P. infestans. The tissues of the stem nearest the 

 mother tuber were softer than those higher up, which would indicate 

 that the infection was of longer standing in that section of the stem. 



