60 MICROSCOPY FOR BEGINNERS. 



and refuses to move again. The streams in two cells 

 lying side by side may flow in the same or in opposite 

 directions, with only the thin wall between them. What 

 causes these remarkable movements is not known. Cold 

 seems to retard, and warmth to hasten the flow, and 

 often, when the chlorophyl has increased so that the 

 green grains crowd the cells, the circulation ceases, ap- 

 parently because the chlorophyl has not enough space 

 for free movement. The botanists call this circulation 

 of the protoplasm cyclosis. It is also finely seen in the 

 long, narrow, ribbon-like leaves of Vallisneria, an abun- 

 dant and common plant in slowly flowing streams. 



To show the cyclosis, the Anacharis leaf needs only 

 to be cut close to the stem, placed in the cell in water, 

 covered by a thin glass, and examined by a high-power 

 objective. The one-inch glass will not show it. . 



The plant is a fruitful source of supply for our two 

 common species of Hydra (Chapter YL), which often oc- 

 cur there so plentifully that two or three hang from al- 

 most every leaf. 



SPHAGNUM MOSS (Fig. 15). 



On the wet shores of shady bogs this pale -green 

 moss grows in great patches, thick, soft, and elastic. It 

 is a beautiful plant anywhere, but it is especially so 

 when it appears greenly glimmering beneath the shallow 

 water, while the shadows of elder and azalea, and the 

 broad leaves of the tangled smilax vines, make the 

 neighboring thicket dim and cool, even when the hot 

 sun smites the bordering fields. In such pleasant sur- 



