mm 



PLATE Vn.— COSMARIUM BOTRYTIS— a Desmid. 



(After Dodel-Port and De Bary.) 



Desmids (Gr. desmos, a bond) are unicellular Algae, of a green colour, found in fresh-waters. They are remarkable for their 

 beauty and symmetry of form, exhibiting division into two symmetrical halves, with a bond or connection between the two — hence the 

 name. They multiply either by division or conjugation. Multiplication by division is the most common, and is that here shown. 



Figures X 1450. 

 Fig. 1. Adult form in front view. 



The cell is divided by a deep constriction into two symmetrical halves. Each half looked at from the side is 

 round, inclining to ovaL The Cell-wall is marked by tuberosities scattered over it, giving it a remarkably elegant, 

 - sculptured appearance. Each half-cell contains protoplasm coloured green, two round starch grains, each with four 

 chlorophyll-bands or green-coloured protoplasm lying over it, and several clear vacuoles containing a number of oscillat- 

 ing granules. 



The Protoplasm generally is of a pale-green colour, only it becomes clear in the middle where the nucleus 

 lies. The plates of protoplasm, the so-called "chlorophyll-bands," are of a dark-green colour, and only one-half the 

 number are seen in this view. 



The Starch-grains are symmetrically disposed, two being on each side of the principal axis. 



The Vacuoles are filled with fluid, and lie between the starch-grains and the cell-wall. There are also a number 

 of oil-drops scattered throughout the mass. 



Figs. 2, 3, and 4. Multiplication by Division — 



The central constricted portion lengthens, and a delicate partition forms, dividing the whole into two equal 

 halves, as in Fig. 2. 



Next, the daughter-cells thus formed increase in size, and the contents of each original portion begin to pass 

 over, as in Fig. 3. 



Finally, the newly-formed portions assume the dimensions of the old, as in Fig. 4, till, in about ten hours, two 

 full-grown individuals appear. 



