FUNGUS OCCURRING IN PULVINARIA INNUMERABILIS. 305 



THE SYMBIONTS OF THE HALF-GROWN PULVINARIA. 



In early April the overwintered cottony maple scale-insects are 

 partly grown and may be found attached to the bark of small 

 twigs on the food plants, which consist of various maples and a 

 few other w r oody plants. At this time they are nearing the end of 

 their period of hibernation and do not yet exhibit any active 

 growth. 



If a specimen in this condition be crushed on a slide in normal 

 salt solution, the symbionts may be readily seen free in the liquid. 

 They are heavier than the medium and fall next to the slide, thus 

 separating from the released fat globules which accumulate above, 

 against the cover-slip. In such a preparation all the organisms 

 appear to be in the liquid, as those in the fat cells are not readily 

 discernible on account of their hyaline nature. This, no doubt, 

 accounts for the statements that the symbionts occur in the lymph 

 rather than in the tissue. 



In sections it is evident, however, that the organisms are absent, 

 or at least very nearly so, from the blood and that they are very 

 generally distributed through the fat body, imbedded in the adi- 

 pose cells. They are usually spaced in a quite regular way show- 

 ing that they migrate or at least change their position in the cells 

 subsequent to multiplication. The density of distribution is well 

 indicated in the drawing (Fig. I, A) which is made from a section 

 of 6 /x. in thickness where all of the symbionts present have been 

 sketched. The photograph on Plate I., Fig. i, is made from a 

 typical cross-section through an entire insect, in which the sym- 

 bionts appear as minute oval dots. CM Plate I., Figs. 2, 3 and 4, 

 are reproduced several small areas of the fat-body viewed at 

 higher magnification with their symbiont inclusions. Sketches 

 of a few still more highly magnified symbionts are shown in Fig. 

 i, B. Here it will be seen that they are extremely variable in size 

 and shape, but always quite distinctly oval in form with one pole 

 more acute and the opposite one more rounded. They vary in 

 length from 1 0-16.7 /x by 5-6.5^ in width, with an average size 

 of 10-12.5 /A by 5.7^. Budding forms are frequently present, the 

 bud developing at the narrow pole and separating either as a small 

 oval, or more rarely rounded, cell. The buds at the time of sepa- 



