1881,] 



MICEOSCOPICAL JOUKNAL. 



25 



Mr. J. Browning. When using blue 

 light, produced by ammonia sulphate 

 solutions, I have resolved, by means 

 of this monochromatic bull's-eye 

 Amphipleura, with objectives in my 

 possession, which will hardly show 

 Pleurosigma angulatum under or- 

 dinary condenser illumination. 



V. — Some time ago, Mr. J. E. Ing- 

 pen, on my behalf made a commu- 

 nication to the Club in regard to a 

 growing slide I had devised for some 

 special researches I was following at 

 the time. Some difficulty seems to 

 have been found in the making of 

 these slides, so that it is with pleasure 

 I now offer a still more simple con- 

 trivance for obtaining the same 

 results. Here is the receipt : Take 

 an ordinary glass slip with a circular 

 hole, say half an inch or more in 

 diameter in the middle ; lay this slip 

 on an ordinary glass slide, not perfo- 

 rated. Then grease the top of the 

 upper or perforated slide just a little 

 way around the circular hole, and 

 join the two slips of glass by means 

 of two rubber rings. The object is 

 then placed on a thin cover-glass, 

 somewhat larger than the hole in the 

 slide ; it is then covered by a thin 

 glass cover, ^ inch in diameter ; the 

 whole is then turned down and fast- 

 ened to the slide by the adherence 

 with the grease, while the small cover 

 prevents the running of the liquid. 

 The plant or animal under examina- 

 tion finds itself confined in a sort of 

 miniature Ward's case. When not 

 under observation, the growing slide 

 is laid flat in a shallow plate with 

 water just above the line of junction 

 of the two slips of glass, where, by 

 cdpillarity, it creeps up to the central 

 cell, where evaporation keeps the con- 

 tained atmosphere in a state of con- 

 stant and healthy saturation. 



VI. — Copal Varnish. I find this 

 varnish dries very rapidly if slightly 

 heated, or even if placed on a pre- 

 viously warmed slide. I have many 

 hundred slides of diatoms prepared 

 in copal varnish, and my friend, Mr. 

 Van Heurck, of Antwerp, who was 



the first to use this material, has 

 many thousands. The varnish to be 

 used is what is called the "pale 

 copal," and its consistency ought to 

 be that of oil. It is much pleasanter 

 to use than Canada balsam, does not 

 make bubbles, and its refractive index 

 is not very different from that of 

 balsam, and does not interfere with 

 the resolution of diatom markings. I 

 have of late made many preparations 

 in copal dispensing with the cover- 

 glass altogether. The drop of copal 

 is placed on the diatoms and heated 

 slightly over the spirit lamp. It soon 

 takes the consistency of amber, and 

 is hard enough to sustain wiping and 

 brushing with a soft brush with impu- 

 nity. The optical aberrations pro- 

 duced by the cover-glass are thus 

 done away with. 



I hope at some future day to add a 

 few more " Receipts for Microsco- 

 pists " to the above list ; may the 

 above, however, in the meantime lead 

 to similar communications from 

 brother microscopists. 



o 



Form-cycle of Gloeocystis.* 



BY PAUL RICHTER. 



The fact that different fresh-water 

 algae, such as the free spores of 

 Draparnaldia, the resting conditions 

 of Chlamydomoftas, and the early 

 stages of Urococcus, form enveloping 

 membranes like Glccocysiis, has made 

 the limitation and determination of 

 the latter genus very uncertain, if 

 the habitat is not known. Whoever 

 has been engaged in collecting algae, 

 will fully agree with me, that local 

 circumstances often influence the 

 forms of certain algae in a very special 

 manner, and that the habitat pos- 

 sesses a signification here, just as in 

 the case of the other plants. For ex- 

 ample, Gloeocystis, according to 

 Nagcli and to the author {Einzellige 

 Algen, p. 66), occurs upon moist 

 wood-work and stones, not free in 

 water or upon submerged objects, or 

 among other algae like ClamydomonaSy 



* Translated from Hed-wigia. 



