STUDIES ON CLUBROOT OF CRUCIFEROUS PLANTS 423 



where diseased roots were buried had become so badly infected that they 

 began to wilt and turn yellow, all the plants were discarded and the plat 

 was reseeded. Different crops of seedlings were thus grown for almost 

 a year, and, altho there was a gradual spread of the organism, it was 

 only by careless watering and planting that the pathogene was carried 

 in the soil to all parts of the box. 



Cabbage seeds were sown in a greenhouse plat in rows ten inches apart, 

 the bottom of each trench being first lined with infested soil. Halfway 

 between these rows were sown other rows, in the trenches of which no in- 

 fested soil was placed. The inoculated plants (fig. 96) became infected 

 at a very early stage, while the plants that were only five inches away 

 from the spores remained healthy until they were almost mature. 



A few authors (Carruthers, 1893, and others) claim that wind is an 

 important agent in spore dissemination. This may be true in light, 

 loose soil, and in localities where strong winds prevail, but in none of the 

 observations made by the writer was there a single case in which the 

 presence of the organism could be explained on this basis. On the other 

 hand, many of the fields showed that if the soil were not transferred 

 by some agent other than the wind the pathogene did not spread. On 

 Long Island, New York, a certain field was observed, one corner of which 

 was slightly lower than the adjoining part. This corner had been used 

 for a garden until clubroot became so prevalent that the plat was no longer 

 profitable for the raising of crucifers. It was then tilled with the remainder 

 of the field for three years while various crops were grown, cabbages 

 not being planted again until the fourth year. A space only slightly 

 larger than the original garden then displayed the presence of clubroot. 

 If wind had been an important agent it would have had an opportunity 

 here, for the land was almost level and the soil was very loose. This 

 was only one of several cases in which the same conditions were observed. 



SPORE GERMINATION 



Very few persons have been successful in germinating the spores of 

 Plasmodiophora Brassicae, and of those few who have been so fortunate, 

 still fewer have seen the actual process. Woronin (1878) gives a brief 

 description and a series of illustrations which have been copied by nearly 

 all later writers on this phase of the subject. The general experience, 

 however, seems to have been like that of Maire and Tison (1911) while 

 working with Tetramyxa parasitica Goebel. They saw only one spore 

 actually germinating, and after a very long, tiresome vigil they left it 

 for a few minutes. On returning from their temporary absence they found 

 that the phenomenon had been completed. Notwithstanding these diffi- 



