Clark — Holophytlc Plankton of Lakes Atitlan and Amatitlan. 95 



hand in all stages of growth from that of a relatively small glohular colony 

 to the last stage of old age, and they agree with the stages given in the 

 life history of Clathrocysiis aeruginosa (Kuetzing). 



Associated with this plant and apparently intimately connected with its 

 life history is a minute filamentous alga which I identify with some douht 

 as Anabxna stagnalis Knetz. to he more fully discussed later on. The 

 colonies in their earlier stages are usually free from the Anabsena or 

 nearly so, but by the time they have reached middle size, and while 

 the contour of the surrounding jelly is still unbroken, the greater number 

 of colonies are more or less infected, many of them containing the Anabsena 

 filaments in greafnumbers. After the jelly has disappeared, the Clathro- 

 cystis cells still continue to cohere. In this stage the filaments of the 

 invading alga are very much in evidence, forming indeed a very con- 

 spicuous part of the colony, projecting from the periphery of the cell- 

 mass thickly in all directions, giving it a bristly appearance. The 

 mingled mass of filaments and globular cells remind one strongly of sec- 

 tions of lichens with their gonidia and accompanying hyphal filaments. 



It does not appear that the Anabsena filaments exercise any injurious 

 influence on the Clathrocysiis cells; they appear to be merely aulophytes. 

 Some colonies that contain them in great numbers appear pale, but the 

 greater number appear healthy and robust as before infection. The 

 filaments, moreover, are not closely applied to the Clathrocysiis cells but 

 lie loose in the jelly. It is probable that they have a good deal to do 

 with the breaking down and deliquescence of the jelly, but this has 

 always been described as a normal event in the life history of Clathro- 

 cysiis colonies, and no accompanying organisms have been mentioned. 



The specimens of Clathrocysiis at hand agree almost perfectly both in 

 form and color with the figures of Clathrocystis aeruginosa given in 

 Griffith and Henfrey's Micrographic Dictionary, pi. 5, fig. 9d, and with the 

 other figures in the same plate except in color. They agree fairly well 

 with Wolle's figures (plate CCX, figs. 17, 18, 19, F. W. Algae), except 

 that the colonies are usually broken up into lobate masses instead of 

 being clathrate. The cells of C. aeruginosa are variously given as 2.5 to 

 3.5 and 3 to 4m. those of C. robusta attain a diameter of from 6 to 9/u. 

 In both species the colonies vary greatly in size; they probably attain 

 much larger size when there is little wave-motion. 



Probably whatever is true of Clathrocystis aeruginosa in general in 

 relation to the other life of the lake is true of this. The behavior of that 

 species is such that one can hardly speak of its abundance in general 

 terms, or make general comparisons between different bodies of water 

 except in cases where it has been under long periods of observation, as 

 it is likely to be very much in evidence some days and rare at other 

 times. Apstein (Das Siisswasser plankton, 135) gives an interesting 

 discussion concerning C. aeruginosa, noting its great abundance on a 

 certain occasion, and discusses its probable relation to fish life. He 

 remarks in substance that it is a common opinion that C. aeruginosa, 

 with other algee that form wasserbluethe, is injurious to fishes, but asserts 

 that while this may be true in small ponds, that it is certainly not true 



