PLANTS IN" PONDFISH CULTURE. 9 



mean"^liile, in the meshes of the fihiments. This alga compares 

 favorably with M. genufeoca as a food producer. It appears in 

 abundance in the ponds later in the season than the foregoing species 

 and has been observed repeatedly in the examination of the larval 

 food of Orthocladius, Pseudochironomus, and Stratiomyia. 



Spirogyra species are generally a vivid gi'een. They more often 

 form a part of an algal complex, though they may occur nearly pure 

 in round mats of varying size. They can be identified easily by the 

 slimy, silky feel of the single threads or filaments. When held out 

 of the water the single threads drip and curl up on drying. 

 Sfirogyra weberi may develop in a pure stand enveloped in a mass 

 of transparent jelly. 



(EdogoniuTn martenicense often forms the upper layer on the mat 

 of Cladophora. Upon aging, it fades to a pale yellowish color and 

 acquires a soft cottony feel. Chironomids are active feedere upon it. 



(E. sp.*^ does not form a mat but occurs as an epiphyte on the 

 larger aquatics and on the coarser filamentous algfe. The slender 

 naias {Naias fieadlis) and the water-weed {Elodca cmmden.^is) may 

 become completely swathed in it by midsummer. It is an extremely 

 small form of OEdogonium which in the aggregate takes on an olive- 

 green look. It has the characteristic cottony feel. All things con- 

 sidered, it doubtless affords forage to a greater number of pond 

 herbivores than any other alga of the ponds. Chironomids, snails 

 (Planorbis and Succinea), and the blunt-nosed minnows, as indi- 

 cated by their food contents, show a preference for this alga, 



Pithojjhora ccdogonia var. vauclierlouleH consists of short filaments 

 which on aging look and feel like coarse, dark hair. It is generally 

 to be found with Cladophora and in the mat-forming stage occupies 

 tlie stratum beneath it or becomes interwoven with it. 



Cladophora crispata forms the coarsest and thickest algal mats in 

 our ponds. The mats, or portions of tliem, have a coarse, heavy look 

 and a harsh feel. When the mat is lifted out of the water it feels 

 tough and gives one tlic impression of handling wet, coarse, brown 

 paper or coarse loosely-woven cloth. 



IJydrodictyon rrticuhitiun, or water-net, is easily distinguished 

 when floated out on the hand by means of the characteristic four to 

 five sided meshes. It may form in sufHciont abundance to produce a 

 heavy mat covering the surface of small ponds. 



These " rough and ready " field characters should assist the un- 

 initiated in discriminating the most common and widely distributed 

 representatives of the mat-forming alga; of our pond waters. It is 

 recognized of course that the microscope, together with keys and il- 

 lustrations, is the only sure method of identification. 



BOSMINA AND VOLVOX ASSOCIATION. 



The plankton studies in pond 2D showed a conspicuous association 

 of the small cladoceran, Bosmina, Icmgirostns, and the green alga, 

 Volvox, species perglohator and xpeniMtoHpIui ra. 'i'hc association of 

 these organisms. Bosmina and Volvox, is important in terms of fish 

 food. The Bosmina afford a direct means of subsistence to the young 

 bass : and the Volvox, thi-ough their contribution to the food supply of 

 the Bosmina, an indirect one. 



"A valuable forago Bpcrlos unldcntHicd ti> ri;iic i.nt probably near howardil. 



