PROTOCOCCUS PLUVIALIS. 551 



part of the drop of water in which they may be placed, 

 furthest from the light. 



Too strong sunlight, as when it is concentrated by a 

 lens, at once kills the zoospores. A temperature of 

 undue elevation is injurious to the development of the 

 more active vital activity, that is to say, for the formation 

 of the zoospores ; whilst a more moderate warmth, parti- 

 cularly that of the vernal sun, is extraordinarily favor- 

 able to it. Frost destroys the motile, but not the still 

 zoospores. 



When kept in the dark, the zoospores become blanched, 

 that is to say they acquire a pale green colour, almost 

 without granules or red substance; the chlorophyll- 

 vesicles, moreover, are not visible, so that the contents 

 of the primordial cell appear as a soft, homogeneous, 

 substance. The membrane is of a soft gelatinous con- 

 sistence ; the motile zoospores continue their movement 

 uninterruptedly, without, as is usual, sinking to the 

 bottom, or passing into the still form, or into the stage of 

 segmentation. 



Under the influence of -light, the cells give out a large 

 quantity of oxygen. It is perhaps the continued greater 

 evolution of gas by the motile spores, as compared with 

 those in the still condition, that causes them by pre- 

 ference to rise to the surface, and the latter to sink. 



Strychnine and morphine, even in the proportion of 

 1 part to 150 parts of water, had no immediate influence 

 on the motion and life of the cells, whilst a solution 

 of iodine so weak as not to render starch anywhere 

 visible, acts at once as an active poison. Cohn observed 

 that when he had starch granules together with motile 

 zoospores on the object glass, and added a very dilute 

 solution of iodine, the motile cells, by their death, shew 

 themselves to be much more sensitive reagents with 

 respect to iodine, even than starch. Rapid evapora- 

 tion of the water in which the motile forms of Proto~ 

 coccus may be contained, kills them, at once, but a more 

 gradual, such as takes place in deep glasses, causes 



