316 CHARLES T. BRUES AND RUDOLPH W. GLASER. 



than detrimental as the fat is not broken down until the time that 

 it would normally disintegrate to supply nourishment for the de- 

 veloping eggs of the coccids. 



Without any definite indication of pathological changes, it 

 seems impossible, therefore, to regard the universally present 

 symbionts as harmful parasites. 



It has also been suggested that they may represent innocuous 

 or indifferent parasites and it is not so easy to distinguish between 

 these and true symbiotic or benign organisms from their effect on 

 the coccids. As a matter of fact it seems necessary to regard all 

 three as steps in an evolutionary process, harmful parasites in 

 their first association, later as innocuous ones and finally as true 

 symbionts. These will follow one another as the host adapts 

 itself to withstand or nullify any ill effects of the parasite until it 

 finally is able to utilize the products of the intruder to further its 

 own metabolic processes. 



Thus it seems reasonable to regard these three types of asso- 

 ciation as not clearly distinct from one another, but as connected 

 by intergrades. 



Since, however, there is good reason to believe that the pro- 

 duction of diastase, protease and lipase by the symbionts may 

 serve to benefit the coccids, the possibility of real symbiosis can- 

 not be excluded. 



There is one point, however, which needs further study. By a 

 minute study of the changes in the tissue of the food-plant ad- 

 jacent to the proboscis of the feeding Coccid, it should be pos- 

 sible to gain much additional evidences upon the changes which 

 undoubtedly occur in such tissue. This we have not had oppor- 

 tunity to undertake. Why the disintegration of the fat-body is 

 delayed till the proper time in the life-cycle of the coccid also is 

 not clear. Since, however, changes in the vegetative character 

 of the symbiotic fungus are initiated in the late spring, it seems 

 probable that they may determine to some extent the quantities 

 of enzymes produced. On the other hand it is evident that the 

 coccid is able to inhibit any excess development of the symbiont 

 as the number of symbiont cells remains very uniform and never 

 seems to increase beyond certain bounds, quite a different condi- 



