1883.] 



MICROSCOPICAL JOURNAL. 



27 



efal days in a warm room, was again 

 taken up and a drop of the water was 

 placed under the microscope. It was 

 very rich in a number of minute algoe, 

 which are to be found in almost every 

 collection, after it has stood for sev- 

 eral days. These minute plants are 

 often very puzzling to the micro- 

 scopist, and the effort will be made in 

 this article to indicate what they are. 

 The reader may obtain them very 

 easily at any time of the year by 

 placing a glass of water with a blade 

 of grass or any bit of plant in a warm, 

 light room, for several days. 



The first alga that will probably be 

 observed, is one that was very abun- 

 dant in the bottle referred to. It is 

 represented in fig. 7 a a' and is known 



Fig. 7. — SCENEDESMUS. 



as Scemdcstnus qiiadricaudatus. Almost 

 invariably, when this plant is abundant, 

 it will be associated with another of the 

 same genus, Sc. acutiis^ c, and in this 

 case we also found Sc. obtusus, b. The 

 first-mentioned species varies greatly in 

 size. The bright-green cells measured 

 from 5.8(U to 14.5JW in length (.00023 

 to .00057 inch) and 2.2jM to 4.3JW in 

 breadth (.000066 to .000172-inch.) 



Every drop revealed a great num- 

 ber of what appeared to be isolated 

 spherical cells, of a green color, meas- 

 uring from 5;* to 6/* in diameter (.000 1 9 

 to .ooo23-inch.) A more careful ex- 

 amination showed that these cells 

 were all connected in groups of two 

 or more, by very delicate branching 



threads, which are often difficult to 

 distinguish. Looking over the slide 

 very carefully we found one aggrega- 

 tion of these cells which showed tol- 

 erably well their mode of growth. 

 It was then seen that a perfect family 

 of these cells is in the form of a sphere 

 or an ovoid mass, the connecting 

 threads radiating from a common cen- 

 ter and branching dichotomously. 

 The plant is known as Dictyosphceriiun 

 E/irenbergianum, fig. ^,ed. It is one that 

 has puzzled us very much in the past, 

 for we could never quite reconcile 

 the descriptions in the books with 

 the plant as observed. It is always 

 described as having a mucous invest- 

 ment, and the cells are said to be 

 oval. In all the specimens we have 

 found the mucous investment had en- 

 tirely disappeared, the families were 

 consequently more or less broken up, 

 and the cells have been quite spheri- 

 cal. Our figure shows the gelatinous 

 investment, but in most cases the cells 

 will be found as shown at fig. 8, e. 



Fig. 8. — Dictyosph^rium. 



In this bottle was one of the larg- 

 est and finest specimen of Amoeba we 

 ever saw. We were using a |-inch ob- 

 jective at the time, and the Amoiba, 

 extending its arms in four directions, 

 reached almost across the field of 

 view. It was very active, and the dis- 

 tinction between the comparatively 

 clear external portion, or ectosarc, and 



