WITH NOTES OjST OTHKE SPECIES. 73 



becomes convex upward, indicating a marked and instantaneous loss of turgescence 

 by the sporangium. All the characteristic phenomena of this stage are much more 

 strongly marked in the species of Achlya {A. Americana and racemosa) than in those 

 of Saprolegnia {8. ferax and sp. indet.) which I have studied. The change may 

 come over a whole sporangium simultaneously, so far as the eye can detect, or it may 

 begin at either end and extend, wavelike, to the other in two or three seconds. 

 While the spore origins seem ordinarily to be quite fused together, careful examina- 

 tion will not seldom show, here and there in the protoplasm, narrow cracks which are 

 the remnants of separating clefts not quite completely closed by the swelling of the 

 origins. Eothert's explanation of this phenomenon seems to accord well with the ob- 

 served facts and with what we know of cell structure in general. He believes that, 

 until the beginning of the stage of swelling, the sporangium wall is lined by a contin- 

 uous protoplasmic layer, and therefore, as in living cells generally, there can be no 

 transfer of liquids between the cavity of the sporangium and the surrounding water. 

 The final extension of some of the dividing clefts between the origins to the wall 

 breaks the continuity of this "primordial utricle," and there is an escape of fluid 

 through the pervious wall and a consequent loss of turgidity. This fluid is distinctly 

 attractive to some forms of Bacteria which may be present in the surrounding water 

 and is, doubtless, the cell sap. Its loss is due, Rothert thinks, to the contraction of 

 the walls which have been distended hj their dense lining, but now become free to 

 assume their natural positions. Measurements show a reduction in the volume of the 

 sporangium amounting in some cases to as much as thirteen per cent. After this 

 loss, water is probably taken up by endosmose, and the mixture of cell sap and water 

 in the cavity of the sporangium is absorbed by the spore origins, whose bulk is so 

 increased that the separating spaces are practically obliterated. The successive 

 absorption and expulsion of this fluid gives rise to the shifting vacuoles. My obser- 

 vation that sometimes in 8. ferax the swelling of the spore origins begins perceptibly 

 later than the incurving of the basal wall, distinctly corroborates this view. 



A very few minutes after the swelling up of the origins, the vacuoles disappear, 

 and the granular appearance returns. They begin again to contract, separating 

 from each other on the old lines, as consecutive observation always shows. The 

 contraction goes on rather rapidly, and the masses become definitely separated as 

 independent spores. While this contraction is going on, small j)ortions of proto- 

 plasm may become cut ofl" from the different spores ; but each is soon taken up, as a 

 rule, by the same spore to which it originally belonged. The significance of this 

 phenomenon will be discussed in connection with the sexual spores, during whose 

 formation it also occurs. The gaps between the spores are widened by their conti'ac- 



