468 Bacterial Disease of Pisiim sativum 



without any very clear definition. The best spore- staining results were 

 obtained from pellicles in liquid media and from growths on potato. 

 The spores can be seen, Plate VII, fig. 14, in the middle or to one side 

 of the oval bodies, so that they appear to protrude. The surrounding 

 substance of the oval bodies seems to swell gradually and become 

 disintegrated so that the spores eventually he embedded in a pseudo- 

 zooglaeal mass. 



I consider the oval bodies to be a kind of involution form as they 

 sometimes vary in size and shape. The germination of spores has 

 not been observed. It is difficult to identify the organism in microtome 

 sections of the older parts of the plants, or in the dry cotyledons, owing 

 to the oval bodies and the pseudo-fooglaeal masses. They can hardly 

 be distinguished from the surrounding heavily stained disorganised 

 tissues of the host plant. In the case of dried peas it is only after they 

 have been kept under moist sterile conditions conducive to germination 

 from 10 — 14 days, or even longer, that the rod stage can be definitely 

 seen. In hand sections of the young succulent parts of the plants, 

 the rods can be readily seen moving about in the cortical cells, although 

 the tissues appear healthy and turgid. The organism can be isolated 

 with ease from the centre of the cotyledons and from the diseased stems. 

 If sufficient care is taken, almost pure cultures can be obtained by 

 infecting tubes of nutrient broth with a small portion of the tissues of 

 the stem or cotyledons, although in the case of cultures from the dry 

 cotyledons the culture tubes have to be kept in the incubator at least 

 10 days before a satisfactory plating can be obtained. The organism 

 grows well at a temperature of 25° C. 



Variability in General Characteristics of Colony. 



Differences in macroscopic appearance in cultures on artificial 

 media do not necessarily mean impurities. Capsular organisms, or 

 those which produce slime, may develop, and mostly do develop, 

 giant colonies (1). Individuals get stuck together, but on the other 

 hand there is always the danger of foreign organisms being caught up 

 in the slime which may prove to be very difficult to separate out. 

 Marshall Ward (14) in 1895 maintained that variation in form, rate of 

 growth, and other characteristics of plate colonies result from much 

 sHghter variations in the medium and other environmental conditions 

 than is generally recognised : also, that* organisms are affected by the 

 vicissitudes to which they have been subjected previous to culture. 

 First platings of the wine bacterium as observed by A. J. Perold(i2) 



