Vol. Xxix] ENTOMOLOGICAL NEWS 293 



appearance of the plants. At this period of the year the large 

 outside leaves drop over on the surface of the water and slowly 

 decay. The smaller leaves in the center of the plant remain 

 alive, but their growth is Yery slow. The usual bright-green 

 color gives way to a lemon yellow. Plants that measure 14 

 and 16 inches in diameter during the wet season diminish in 

 size to 6 inches, or even less, during the dry season. Many of 

 the filamentous roots also seem to decay and drop off during 

 the dry season. During this time large plants are often found 

 having less than 10 per cent, of the number of rootlets that 

 are usually present at other times of the year. From observa- 

 tions made we consider that these changes are caused by the 

 dry hot winds, burning sun and lack of rain and moisture of 

 the dry season. Apparently the leaves are unable to take up 

 sufficient moisture from the water in which they grow to with- 

 stand the effects of the wind and sun for any length of time. 

 A certain amount of rainfall seems to be necessary. Plants 

 growing in small sheltered coves, where they are continually 

 shaded from the sun and protected from the action of wind 

 and current, remain green and vigorous throughout the year. 



On nearly all arms of the lake that reach back into former 

 river valleys, portions of the surface will be found thickly, cov- 

 ered with Pistia plants. In the Cano and Pescado River reg- 

 ions tightly packed masses of plants extend over the surface 

 from shore to shore, covering the water for mile after mile. 

 In the lower parts of the Pelanque, Aguadiente and Chilibre 

 districts several square miles of Pistia may be found. The 

 lake portion of nearly every river region on either side of the 

 lake has its quota of plants. 



We have made soundings at points in the Cano River dis- 

 trict where these plants were so thickly massed together on 

 the surface that it was necessary to separate them in order to 

 see the water, and found a depth of 34 feet under them,. 

 However, although growing and rapidly multiplying on the 

 surface of deep water, they reach a greater degree of luxuri- 

 ance when in shallow pools of stagnant water, bordered by 

 thick forest growths which afford shade. In places of this 



