1891.] MICROSCOPICAL JOURNAL. 85 



sufficiently account for the varying breadth of the bands in the filamen- 

 tous species and the diversity of size in the frustules of the free forms, 

 without obliging us to suppose that a growth or aggregation takes place 

 in the siliceous valve when once.formed. • Starting from a single frustule, 

 it will be at once apparent that if its valves remain unaltered in size 

 while the cell-membrane experiences repeated self-division, we shall 

 have two frustules constantly retaining their original dimensions, four 

 slightlv increased, eight somewhat larger, and so on, in a geometrical 

 ratio, which will soon present us with an innumerable multitude con- 

 taining individuals in every stage, but in which the larger sizes pre- 

 ponderate over the smaller, and such are the circumstances ordinarily 

 found to attend the presence of large numbers of these organisms."* 



I say nothing about his reasoning, but simply call attention to these 

 two points: i. That he declares that in a filament of many hundred 

 frustules the difference in size is scarcely appreciable ; and, 3, that when 

 we find these organisms present in large numbers the larger sizes pre- 

 dominate over the smaller. 



So much, then, for this mode of reproduction, namely, by division. 

 The other is by conjugation, but I shall not enlarge upon it, simply 

 mentioning that Wolle says there are three methods : i. Two frustules 

 producing a single sporangium ; 3, two frustules producing two sporan- 

 gial cells ; 3, a single frustule, by differentiation of contents, producing 

 one sporangium ; and the last he says is the most common of the three. 



\To be continued..^ 



Microscopy for Amateurs. 



By T. CHARTERS WHITE, 



QUEKETT CLUE. 



{Continued from page bj.^ 



Infusoria. — To pursue this branch of study with convenience and 

 comfort, sundry accessory apparatus will be required. One may stand 

 by a promising pool and gaze with longing eyes at an aquatic plant, 

 which is loaded with life, but without the means of getting it. A 

 collecting-stick must be obtained. This looks like an ordinary walking- 

 stick, but artfully conceals joints in its interior by which it can be length- 

 ened. The student takes it on his walk. But the stick is not enough ; 

 he must have something to hold his infusorial life. Nothing answers 

 this purpose so well as the screw-top York bottles, obtainable of most 

 chemists. One or two of these are carried in the pocket. Sold with 

 the stick is a metal ring, having a screw thread within it which fits the 

 screw on the York bottle. By another screw on its side it may be 

 firmly and securely attached to the stick, so that when the bottle is 

 screwed into the ring, and the ring is screwed to the stick, and the joints 

 of the stick are joined, we have a piece of apparatus as long as a fish- 

 ing rod, but stifter, and which will reach out to the middle of any or- 

 dinary pool. But you say, " How will this get up the water plants I 

 want ? " In the collecting kit you ought to find a sharp sickle-shaped 

 hook, which will screw into the end of the stick when the screw carrv- 



*Rev. Mr. Smith's Synopsis, Bin. Diet., vol. i, p. xxxvi. 



