16 S. E. A. McCallan 



of water will of necessity vary greatly. Although meteoric waters — 

 that is, rain or dew — will be present under natural conditions, it is felt 

 that they are not ideal for tests because of their great variation in com- 

 position. Distilled water would seem to be the most suitable, provided 

 the spores will germinate well in it, Doran (1922) found that the dis- 

 tilled water which he used lacked aeration, and unless it was artificially 

 aerated it reduced germination. Lack of aeration has not proved a 

 serious obstacle in the writer's studies. All the spores that he tested 

 required precipitated moisture for germination. In some cases, spores 

 germinate equally well merely in a moist atmosphere (Doran, 1922). 

 Certain types of spores are placed in suspension in water only with the 

 greatest difficulty, and as yet no method has been devised to satisfactorily 

 overcome this. 



Concentration of spore suspension and oxygen relations 



AW workers have found that the presence of oxygen is essential for 

 normal spore germination (Uppal, 1926). In all probability there is 

 never an excess of air dissolved in the water, as far as the spore require- 

 ments are concerned. Hence the size and shape of the drops of water 

 on the slides must be considered. It has generally been found that the 

 flatter the drop, the better will be the germination. Also, the drops 

 should all be of the same size in order that the oxygen relations and 

 the possible staling effects may be constant, Finally, unless the drops 

 are of the same size, surface and vapor-tension phenomena will result 

 in the larger drops increasing in size at the expense of the smaller ones. 



Doran (1922:332) noted " the injurious effect of the presence of fungous 

 spores on the germination of the spores of other fungi." He attributed 

 this to a competition for oxygen. He states: " When there is lack 

 of sufficient oxygen for all, only those spores which require the least will 

 germinate." Obviously, only one kind of spores should be present in 

 the drop. 



Because of the ox3 T gen limitations and the staling effect (Wallace, 

 Blodgett, and Hesler, 1911:173), there is a limit also to the number of 

 spores that will germinate in a given drop of water. Hence there is an 

 optimum spore concentration. As a general rule it may be said that the 

 fewer the spores, the higher is the percentage of germination. However, 

 if the number of spores is very much reduced, the probable error for germi- 

 nations in a single drop will become unnecessarily high. Therefore, in 

 making up spore suspensions in water the object should be to obtain as 

 high a concentration of spores as is possible without unduly reducing 

 the germination. 



The relations of spore concentrations to germination for Botrytis allii 

 are shown in table 2. In this, as in all succeeding tables, the number of 



