the ' Crown-Gall ' Fungus of Lucerne 361 



as the galls are not easily observed until the plant is removed from 

 the soil. A number of normal, leafy shoots may develop on the 

 plant close to the galls, and in hot weather it is often noticed that 

 these shoots become yellow and show signs of wilting: in this way 

 it is possible to pick out infected plants in a field. The most con- 

 venient starting point for a description of the parasite is the resting 

 spore and its germination. Mature spores are globular, flattened 

 at one pole, the average dimensions being 30 yu, by 45 /a, with an 

 extremely brittle wall nearly 2 fx thick, of a rich golden brown colour, 

 Hned with a thin colourless membrane. Only a very small per- 

 centage of the spores examined were induced to germinate; hanging 

 drop cultures were started with different hquid media containing 



501 L. 



ARTIFICIAL 

 INFECTION 



Fig. 1. 



spores from galls of various ages, some of which were more or less 

 completely rotted. Some spores were treated previously with lactic 

 acid, pepsin and other reagents which have been found to induce 

 germination in other cases; others again were exposed to low tem- 

 peratures, but consistent results were not obtained. It was however 

 found that very slight pressure was often sufficient to start germina- 

 tion in certain cases, and that the most easily germinated spores 

 were obtained from galls which had become rotted owing to the 

 action of mould fungi (often Fusarium sp.) and bacteria. The de- 

 velopment of external zoosporangia as described by C. E. Scott* 

 was never observed ; the first sign of germination being a vibratory 

 motion of the spore contents visible through the wall. This may 

 continue for half an hour, but as a rule the escape of zoospores begins 

 almost at once. Irregular cracks appear in the spore wall ; a portion 



* Scott, C. E. (1920). Science, N.S., No. 1340, pp. 225, 226. 



