SWARM-SPORES AND EMULSION-FIGURES. 609 



the water, and the result of which was formerly also ascribed to their active 

 movements '. 



In stagnant pools, ponds, hollows in stones, &c., the water is often found, 

 especially in the spring time, to be coloured of a more or less intense green by 

 innumerable swarm-spores. If such green water is poured into an ordinary plate 

 or other shallow vessel, and placed in the neighbourhood of a window, it is 

 observed after some time that almost all the swarm-spores are collected at the margin 

 of the vessel turned towards the window; occasionally, as shown in Fig. 359^, 

 there appears at the same time, floating in the middle of the liquid, a green figure, 

 the apex of which is turned towards the window. If the fluid contains at the 

 same time large and small swarm-spores (macro- and micro-zoospores), e. g. of 

 Hcemafococciis plmn'alis, &c., all the micro-zoospores are found after a little time at 

 the margin of the water turned towards the window, and also at the surface ; 

 while the macro-zoospores are collected at the margin of ihe vessel which is turned 

 away from the window, and also at the bottom of the water. If, on the contrary, 

 the vessel referred to is allowed to stand in the middle of a room where the 

 temperature is equable, or even outside the building where the temperature is 

 everywhere alike, cloud-like aggregations of swarm- spores are formed in the centre 

 of the liquid, and these may present the most various shapes, differing, however, 

 from the preceding in that neither the outer nor the inner margin of the vessel 

 seems to be preferred. On the contrary, the swarm-spores form cloud-like col- 

 lections, as rounded groups extending from the surface to the bottom of the 

 liquid, or as concentric circular clouds coexistent with radiating and rounded 

 groups, as in Fig. 359 B, or even as reticulate figures extended over the whole 

 vessel. 



I found now that both kinds of aggregation of swarm-spores may occur in the 

 fluid in the most varied manner, and that they appear also when the vessel is covered 

 with a glass bell-jar or with an opaque card-board receptacle. Light, as such, 

 exerts no influence on the formation of these figures ; on the other hand, it is the 

 currents formed in the water by the warming and cooling which produce the 

 aggregations of swarm-spores referred to. If the vessel in question stands at a 

 window, and especially when it is cool or cold outside while the chamber is heated 

 by a fire, then a continual streaming of the water goes on in the plate or vessel, 

 so that the cooled water at the margin of the vessel next the window sinks to 

 the bottom, flows thence to the opposite margin, and then ascends and streams 

 on the surface as warmer water to the margin of the vessel next the window again. 

 This continually circulating current of water carries the swimming swarm-spores 

 with it, and causes, in combination with their active movement, their collection in the 

 manner described, either at the surface at the colder margin next the window, or at 

 the bottom of the vessel at the warmer margin turned towards the chamber. That 

 it is hexe actually and simply a matter of a diff"erence in temperature between the 

 two margins of the vessel, and not of illumination, follows not only from the above- 

 mentioned fact that the phenomenon occurs even under an opaque receptacle, but 



* Sachs' ' Über Emiihioiisßgurcn und Grtippiniug der Schwärinspcreii im U'asser,' Flora, 

 1876, p, 241. 



[3] Rr 



