ZOOSPORES IN THE SAPROLEGNlEiE. 431 



tractile vacuole of an Amoeba is seen to disappear. In a starved 

 sporange the protoplasm contracts into a bossed gut-like mass 

 towards the centre of the sporange ; for the cell wall is rather 

 thickened and rigid, so that it cannot present the contraction so 

 marked in the undetermined S aprolegnia and in a less degree 

 in the Leptoraitus form (which, however, is usually too 

 narrow for easy measurements). I have tried to account for the 

 causes of this curious phenomenon, of which I have just given 

 the first complete description. It occurred to me that the 

 following was a possible explanation. The protoplasm is acted 

 upon in two ways : 1. The tendency of protoplasm to stick 

 together into a single mass. 2. The tendency to aggregate 

 around numerous centres (to form the prominences), aided by 

 the turgesceuce of the sporange. If then the thinning 

 at the intermediate bands went on to complete rupture at any 

 one point, the turgescence would be lost; so the first force 

 would overcome the second, now left unaided by the turgor 

 lost for the moment, and would thus lead to homogeneity ; 

 though the second force ultimately gain the upper hand in the 

 next and last stage. In this case loss of turgescence should 

 always bring on homogeneity. I tried to induce loss of 

 turgescence by De Vries's method of plasnolysis with solutions 

 of cane sugar and of saltpetre. I found, however, that plasno- 

 lysis to a very considerable extent was not sufficient to induce 

 homogeneity. Hence the loss of turgescence must be a 

 concomitant or follower of homogeneity, and not its 

 cause. The explanation had seemed so simple that I was 

 much disappointed at having to give it up ; but the facts were 

 too strong. 



I then experimented with the aqueous solution of eosin, 

 which De Vries has shown does not diff'use readily through the 

 ''Hautschicht" or external layer of protoplasm, nor its internal 

 layer, the '' vacuolar wall." The protoplasm only stains readily 

 at the stage of homogeneity ; whence we may conclude that at 

 this stage the resistant layers do not exist, at least as continuous 

 layers. I think it probable that the Hautschicht and 

 vacuolar walls break up at this stage, and become re- 



