PAPERS ON BIOLOGY AND AGRICULTURE U1 



Indications point to the fact that this lake is filling up : 

 the narrowing circles of willows of different ages, the re- 

 ceding of the shore line on the west end, the great abund- 

 ance of aquatic plants even near the center, and last year, 

 a stranded group of cat-tails near the northwest corner 

 are signs of the developmental process that is being car- 

 ried on. Each season's crop of foliage is packed down on 

 the succeeding layer. The inlet is bringing in constantly 

 its contribution of silt and humus which is caught by the 

 filamentous forms and roots of the hydrophytes or al- 

 lowed to settle in the quiet regions of the center and west 

 end. In collecting material for this survey, we have es- 

 tablished stations in most of the typical regions and have 

 attempted to confine our more intensive study to these 

 smaller areas. 



In the study of the filamentous forms of this area, some 

 material was brought into the laboratory and after the 

 forms were identified, it was allowed to stand undis- 

 turbed; in a short time, another form (hydrodictyon) ap- 

 peared that had not been seen in the material when it had 

 first been examined. This form had developed in the 

 aquaria under conditions very different from those in 

 the pond but had existed there in limited quantities under 

 the unfavorable conditions. It is thought possible that 

 this method of development under conditions different 

 from those of the pond may lead to the discovery of some 

 forms whose development is limited in the pond, or it may 

 lead to some information on the conditions necessary for 

 maximum development and possibilities for growth un- 

 der unfavorable conditions. 



In the more rapidly developing portions, it is possible 

 to make out the following stages; submerged aquatics, 

 floating aquatics, emergent aquatics, swamp society, and 

 finally those of a river flood plain. If the pond is left 

 undisturbed, it will all pass through the above stages. 

 The plants of each stage prepare the way for those of the 

 next one, and in doing so make conditions impossible for 

 their own existence in that particular area. 



In the submerged aquatic society, we find two types; 

 first the free floating, largely made up of desmids and 

 diatoms of the following types, Scenodesmus, Clasterium, 



