EXPERIMENT STATION BULLETINS. 641 



plants were then set in the direct sunlight on a shelf in the window. Five 

 of these plants showed typical infection. 



This experiment was repeated using for inoculation the spore mass 

 witliout making a suspension in water. With a platinum needle a 

 minute portion of this spore mass exuding from a pycnidium was trans- 

 ferred to the leaflets of five plants. The results were similar. All plants 

 were infected after five days. This experiment was performed because it 

 was thought that the drop of spore suspension evaporating, drew the 

 spores into the substomatal chamber. The results indicate that this hypo- 

 thesis is untenable. 



The interpretation of this experiment is rather difficult. There can 

 be no doubt that an extremely small amount of water is necessary to 

 enable the spores to germinate and enter the tissues. This water may 

 be the small amount held upon the leaves, but this is difficult to credit 

 in view of the experiment just reported. The moist air of the substo- 

 matal chamber may be concerned. The mucilaginous spore wall un- 

 doubtedly clings tenaciously to a small amount of imbibed water. A 

 fact to be taken into consideration in the interpretation of these results 

 is that the spores do not germinate in less than 24 hours in a Van Tieg- 

 hem cell or on a moist slide. Combining this with these experiments, 

 the results appear most striking. It is possible that the temperature 

 factor is important in this phenomenon.* It is evident that if the spore 

 reaches the leaf, regardless of the agent involved, the spore will cause 

 infection, providing the temperature is favorable for the development of 

 the mycelium. It may be that in the case of other fungi as well, current 

 ideas on the necessity of water films and dew for long periods in order 

 to produce infection may be based wholly upon inference. 



PHYSIOLOGICAL AND ECOLOGICAL RELATIONS OF THE CAUSAL ORGANISM. 



Germmation: 



To observe the spore germination and subsequent colony formation in 

 various media, the following method was employed: Petri dishes con- 

 taining Van Tieghem cells were arranged according to Duggar's (1910, 

 p. 59) method. Blotting paper was perforated so that small glass rings 

 would be held in place while being sterilized. (Plate 3, Fig. 1). The 

 media used were cornmeal agar (see appendix), potato glucose agar, 

 nutrient broth, nutrient glucose agar, tomato leaf agar, and distilled 

 water. Solid media, from which hanging drops were made, was melted 

 and cooled to approximately 42° 0. An exuding mass of spores was 

 shaken up in each tube. Each Petri dish as described above contained 

 seven Van Tieghem cells. A different medium was used in each Petri 

 dish. Each hanging drop of the medium contained 4-6 spores. 



Thus it was possible to make germination studies and observe de- 

 velopment (under the microscope) until the organism had attained mac- 

 roscopic size. The exact time elapsing before germination was diffi- 

 cult to determine, due to the manner of development of the spores. The 

 first signs are manifested in a pronounced swelling of the spore to al- 

 most twice the original diameter. Kegular, well-defined vacuoles ap- 

 peared surrounded by dense protoplasm, which made the spore look 



*These experiments were performed from August 15 to 31, 

 81 



