14(; 



in the south part of the lake, quite near shore, in 1890. None was seen in 

 1900. 



The water is quite full of minute algae, which is generally kept well 

 mixed up with the water by the constant churning of the waves. In quiet 

 places, however, as near the shore in sheltered places, or among the rushes, 

 these algae, mainly Clathrocystes, form a surface scum. On one day during 

 the latter part of the summer of 1899, when the lake was tolerably low, 

 and after a vei-y calm night, these algae formed an unbroken film or scum 

 over the surface of the lake, except where broken up by the jumping of 

 fishes, etc. The track of the boat and every oar-stroke could be noted 

 across the lake as far as could be seen clearly at all, and, as said above, 

 every place where a fish had splashed up was left as a break on the sur- 

 face. Some phenomenon similar to this is briefly noted in an article by 

 C. D. Marsh, and various names given for it, as "breaking of the meres." 

 or "working of the lakes." (See Science, Vol. XI, No. 268, first column, 

 page 379.) 



DETAILS OF DISTRIBUTION.-In the preceding discussion the only 

 determining condition of plant distribution taken into consideration was 

 the amount of water present in the soil or about the plant; and the various 

 plant gi'oups have been spoken of as if they occurred in regular concentric 

 belts or circles. 



The amount of water has indeed been the most conspicuous influence, 

 and the most easily measured, here as everywhere, and it has been this 

 fact that has determined the conception of the ecological groups, xerophytes. 

 mesophytes, and hydrophytes. It is needless to say, however, that there 

 are multitudes of other influences, such as soil, temperature, and many 

 obscure and perhaps undiscovered influences which operate to make the 

 distribution of the various species tolerably irregular. 



Some of the most noteworthy irregularities will now be discussed 

 more in detail. Only lake plants will be noted. 



SCIRPUS AMERICANV8 (three-cornered bulrush) is found in scattered 

 patches at almost any bit of sandy shore. Along the east and south shox'^s 

 it grows rather thinly and covers only small areas. Its general absence 

 or scarcity along the eastern side of the lake is due in some cases (as in 

 front of the Assembly grounds) to artificial removal. Beginning at the 

 southeastern bend of the lake, however, it extends in large and frequent 

 patches almost to the bend which forms the neck of the lake. At places 

 where it is thickest, as at the gravelly shore at Yarnelle's landing, it is 



