1890.] MICllOSCOPIOAL JOURNAL. 277 



among the simplest members of that simplest class. It belongs to the 

 a/^\c, and to the lowest division of them, namely, the one-celled algcc. 

 It is a protophyte and ranks as low as a protozoan'in'the animal scale. 



What^thcn, is its structure? — Ttis a plantthat lias neither root, stem, 

 nor leaves ; in short, is nothing but a cell which discharges the func- 

 tions of all three. For though a number of these cells may be united 

 together, yet the diatom is just one of them and no more. Fragilaria 

 forms a filament, Meridio?i a spiral, Licmophora a fan ; but neither the 

 filament nor the spiral nor the fan is the diatom. In each case it is 

 one of the joints or cells and no more that is such, ^'et my impression 

 is that there are those who have looked at these forms again and again, 

 who are not awai^e of that fact. The diatom, strictly speaking, is al- 

 ways the simple cell, no matter how many cells are joined together. 

 And properly one should say of either of the above that it is a number 

 of the genus Fragilaria^ or Aleridioti^ or Licmophora. 



W/iat are the chief characteristics of this structure? — A hard 

 outside membrane or wall, and a soft internal substance or protoplasm, 

 termed endochrome because of the granular coloring matter which is 

 diffused through it, except perhaps in the centre, which is often occupied 

 by the nucleus. This latter element, the nucleus, is the most vital part 

 and is intimately connected with the reproduction of the plant. Oil 

 globules are also found in the protoplasm. Add to these features bilat- 

 erality, for the diatom is composed of two nearly S3'mmetrical pieces 

 and motion. So far the diatom is very like a desmid. 



What are its disti/zguishitig characteristics? — First, the presence 

 of silex in the cell wall, the result of which is that the shell remains 

 iiitact after all the contents have been ])urned away. Next, the presence 

 of bands or stripes which form along the inner margins of the two 

 valves ; and finally, the color which is usually yellowish-brown instead 

 of green, though it is not always so, for the young diatom is sometimes 

 almost, if not quite, as green as a desmid ; and this should not be for- 

 gotten. It is only in the later stages of growth that the diatoms are 

 always brown. 



How do diatoms move? — Find that out and you will make a name 

 for yourself in the scientific world, for nobody knows, though manv 

 have tried to solve the problem and imagined they had discovered the 

 key to it. 



Hozv do diatoffis imiltiply? — Certainly by subdivision and conjuga- 

 tion. Possibly, also, by the formation of spores, resting spores, or 

 active zoospores. Now, as to the known process of subdivision. 

 Get a couple of pill boxes, one of which is just a trifle larger than the 

 other, and, taking ofi' the covers, place the boxes together, tojD to top, 

 and one just within the other. Each box represents a valve, and where 

 they are applied the line of junction or'suture. That's your diatom cell 

 or frustule, and inside imagine the nucleus and the semi-fluid proto- 

 plasm. Now suppose the nucleus to divide and the rest of the contents 

 as well at this line of junction, and each half to form another half like 

 itself, but each of the new halves to be formed inside each of the old 

 halves respectively, and the new halves to push the old ones away from 

 each other, the intermediate space on the cell wall being filled by the 

 growth of two bands at the free ends of the old outer valves. Pull your 

 pill boxes apart therefore a trifle, and fill the intermediate space by two 



