FUNGUS OCCURRING IN PULVINARIA INNUMERABILIS. 3!$ 



We have also clearly shown that a proteolytic enzyme and a 

 lipase are produced abundantly by the Pulvinaria symbiont. The 

 possibilities for these to influence the digestion and metabolism 

 of the coccid are more diverse than those presented by the pres- 

 ence of diastase. Both, particularly the lipase, must act upon the 

 adipose cells in which the symbionts occur. We might therefore 

 suppose that they assist in the rapid breaking down of this tissue 

 at the time of maturity when the eggs of the Pulvinaria are rapidly 

 developed. That they may assist in digestion, either in the body 

 or through the agency of secretions injected into the plant is also 

 quite possible, although such indirect action must undoubtedly 

 be secondary if it occurs at all. 



THE GENERAL NATURE OF THE RELATION BETWEEN SYMBIONT 



AND COCCID. 



The symbionts have gradualy come to be regarded rather gen- 

 erally as truly symbiotic organisms, although those who first 

 studied them naturally assumed that their presence indicated 

 some sort of parasitism. There are several reasons why it is dif- 

 ficult to believe that they are actually parasitic. In the first place, 

 not only in Puhnnaria, but in the other species in which they have 

 been found, they are universally present in all the individuals of a 

 species in approximately equal numbers. Many true parasites, 

 e.g., certain Nematode worms, the Protozoan parasites of human 

 malaria, etc., commonly appear with great frequency in the bodies 

 of their hosts, but their occurrence never includes all the individ- 

 uals of a host species, except at certain times and places where 

 parasitism is unusually heavy and assumes the form of an epi- 

 demic. In 'such cases also, the affected population is not in a 

 healthy condition and species so generally affected cannot be ex- 

 pected to represent ones well fitted to survive and become abun- 

 dant. Pulvinaria and other Coccids certainly cannot be placed in 

 such a category. On the other hand the presence of detrimental 

 parasites results in tissue changes or disturbances of metabolism 

 that can be recognized. Such can be seen in the behavior of the 

 fat-body in Pulvinaria and other genera ( Sulc, '11), but as has 

 just been said this is most readily regarded as beneficial rather 



