EXPERIMENT STATION BULLETINS. 639 



quantities tliat the white, glistening mass exuding from the pycnidia 

 was easily perceptible to the unaided eye. This Avas very fortunate as 

 spores could be obtained free from the mycelium and the other substra- 

 tum. (See Plate 4). 



(c) Production of the disease on healthy, plants by inoculation from 



culture. 



A mass of exuding spores from pure culture was shaken up in sterile, 

 distilled Avater. In the first attempt to i)roduce the disease, thirtj'-two 

 plants were used.^ Sixteen plants selected as checks, were sprayed with 

 sterile, distilled waler from a DeVilbiss atomizer No. 2. The spore sus- 

 pension was sprayed upon the other sixteen plants in the same manner, 

 using a similar atomizer. These were all kept under bell jars. 



The result was positive but spots on the inoculated plants were very 

 few per leaflet and small. One check plant also showed infection. INIany 

 leaflets showed no spots at all, and others showed no more than two. 

 Considering the number of spores applied, and comparing the results 

 with the Van Tieghem cell in which 30% of the spores had germinated, 

 the results were not highly satisfactory. 



The following experiment was performed. B}' means of a platinum 

 loop a drop of spore suspension was placed upon a single leaflet; a very 

 small piece of "White Rose" cotton was quickly spread over it. Twenty- 

 five such inoculations were made. The plants were placed in a moist 

 chamber, in Avhich there was an arrangement to produce a fine mist 

 when desired.- In five days every leaflet inoculated showed typical, 

 vvater-soaked, diseased areas. The uninoculated leaflets were free from 

 disease. Pycnidia were evident after ten days and exudation of white 

 spore masses thirteen da3's after inoculation. The advantages of this 

 method of inoculation were: the spores were protected by the cottoji 

 since the moisture collecting on the leaves did not remove them ; the cot- 

 ton indicated exactly where the inoculation was made; every uninocu- 

 lated leaflet was a check on the inoculated leaflet. 



(d) Reisolation and (e) Reinoculation : 



Plates were poured from the exuding spore masses from the pycnidia 

 and reisolations Avere made to tomato agar, nutrient agar, and potato 

 agar. The identity of the recovered organism was determined beyond 

 question. The cultures so obtained were used successfully in subsequent 

 inoculation exi)eriments. 



Infection Phenomena: 



The Period of Incubation : 



Numerous experiments gave entirely concordant results as to the time 

 necessary after inoculation for noticeable lesions to appear. In the 

 extensive experiment reported on page 33 the daily observation required 

 in this experiment gave abundant opportunity for exact record. The 

 first signs of the spots appeared five days after inoculation. In experi- 

 ments where inoculations were made on media of various kinds and 

 these media incubated among the inoculated plants to insure more or 

 less similarity of conditions, it is noteworthy to observe that the colony 

 on tomato agar was approximately the same size as the spot on the leaf. 



'This work was done in a greenhouse where the temperature varied from 18° C. to 

 25° C, and the ordinary moist greenhouse conditions prevailed. 



''A fine jet of water from the tap was allowed to strike the top of a large galvanized iron 



