136 Lake Maxinkuekee, Physical and Biological Survey 



found rather near shore, but the other plants are found throughout 

 the lake at nearly all depths. 



The strictly aquatic plants living within the borders of the 

 lake, being an essential part of the environment of the fishes and 

 other denizens of the lake, were studied in considerable detail. 

 During these studies one of the salient facts that impressed itself 

 continually upon the mind was that the different plants of the lake 

 were aquatic in different degrees. 



Taking the large genus of pond weeds or Potamogetons, for in- 

 stance, we have among them a number of forms with all the leaves 

 fitted only to under-water life, and so constituted that upon ex- 

 posure to the air they crumple up and perish almost as soon as 

 does a fish out of the water. One of the most pronounced species 

 of this type is the handsome P. robbinsii, which lies nearly flat on 

 the bottom, and has become so thoroughly and completely aquatic 

 that it rarely or almost never even ventures a flower-spike up out 

 of the water, but depends almost entirely upon vegetative buds for 

 propagation. 



The large-leaved pondweed, Potamogeton amplifolius, on the 

 other hand, has two well-marked kinds of leaves — thin, almost 

 transparent submersed leaves, and thick, leathery floating leaves. 

 It has a well-developed flower-spike which projects prominently 

 above the surface of the water. 



Finally, in Potamogeton natans, we have a form in which the 

 submersed leaves, though present, are small, undeveloped, and only 

 temporary, the leathery floating leaves being the most prominent 

 and functional ones. Indeed, where these plants grow near shore 

 they are frequently stranded on mud-banks by the receding of the 

 water, and there develop into mud-plants rather than aquatics, 

 with stiff aerial instead of leathery floating leaves. 



Another case is that of the water star-grass, Heteranthera 

 dubia. This frequently grows in several feet of water, entirely 

 submersed, and very closely resembles some of the narrow-leaved 

 forms of Potamogeton. In this situation it rarely flowers. Sprigs 

 broken off by the waves and cast ashore, however, quickly strike 

 root, bear firm aerial leaves, and produce numerous pretty yellow 

 flowers. 



Again, we have one of the species of arrowhead, Sagittaria 

 graminea, the leaves of which form a close rosette at the bottom 

 of the water, these leaves being strictly aquatic and the whole 

 plant, when not in flower, hardly distinguishable from a strict 

 aquatic in all its relations, the seven-angled pipewort, Eriocaulon 

 septangular e. 



