148 THE MICROSCOPE. [July, 



than a human blood corpuscle. They difler from diatoms most 

 strikingly in the cell-wall being soft, and it is said to be composed 

 almost wholly of cellulose (the material of cotton), while the cell- 

 wall of diatoms is infiltrated with silica (the material of glass), 

 which renders them brittle. From other algie they are chiefly 

 distinguished by each cell being composed of two symmetrical 

 half cells joined at their bases, which are sometimes so much 

 constricted as to appear to be two cells, but as the protoplasm 

 (bioplasm or life substance) circulates from one to the other they 

 really form but one individual cell. Desmids differ from one an- 

 other in shape, size, markings, and the presence or absence of 

 processes, angles, spines, etc. Over thirteen hundred of them 

 have already been described, and while it seems really wonderful 

 that so many and beautiful forms can be fashioned from a single 

 cell, the student will readily understand that the possibilities are 

 almost infinite. Desmids have a small power of motion, which 

 is usually so slight as to escape observation, but it is sufficient to ex- 

 tricate them from sediment when they are not too deeply buried. 

 While desmids may be found at any season when we can get 

 at the bottom of shallow ponds, the best will be found when all 

 plant life is in vigorous growth. Sink-holes which have no vis- 

 ible outlet, and from which the water nevjer entirely disappears, 

 are generally excellent gathering places. Shallow ponds, still, 

 shallow coves of lakes, mill ponds, and quiet pools in streams are 

 promising resorts. They may often be plentifully found clinging 

 to the long water- weeds, from w4iich they may be detached by 

 dipping the weeds into a bucket of water and rinsing them up and 

 down. The size of the pool often bears no relation to its impor- 

 tance. A small cavity in low ground, from which the moisture 

 almost but never quite disappears in times of drouth, and which 

 is scarcely two feet across, has produced two new forms. It was 

 formerly the bed of a small granite boulder, and is lined with a 

 growth of sjDliagnum moss, from which it seems always possible 

 to squeeze a few drops of water, and when driest yields semi- 

 cells of the plants free from chlorophyll and in best condition for 

 examination of their marking's. A small deoression in a similar 



O J. 



place, apparently made by the pressure of an ox's foot, was a 

 valued treasury for several months, though it gaye no forms new 

 to science. 



The outfit for gathering samples of water need be neither large 

 nor expensive. A dozen one-ounce wide-mouthed round-shoul- 

 dered jDi'escription vials, costing, with their necessary corks, 

 twenty-five cents, a pond-stick cut from the roadside, a hand mag- 

 nifying glasss, costing another quarter, and a small memorandum 

 book are the only requisites for preliminary search. The pond- 

 stick is usually a grey birch about three-quarters of an inch in 

 diameter at the large end, which is flattened on opposite sides for 



