42 A HALF-HOUR WITH THE 



test-objects, for testing the highest powers of the 

 Microscope. 



Whilst living, the diatoms possess the power of 

 moving about, and in some of them, as well as the 

 desmids, a movement has been observed of the 

 small particles in their interior. The diatoms are 

 generally of a brownish or brownish-yellow colour, 

 which seems to be due to a small quantity of iron 

 in their composition. They are increased in the same 

 way as the desmids, by the production of new cells 

 between the parent frustules (Figs. 135, 136, PL 5), 



Sometimes, attached to the bottom of a pond or 

 river, or growing from immersed objects, or floating 

 about in the water, will be found long green fila- 

 ments. These are the fronds of confervse. All 

 forms of these and they are very numerous will be 

 found most bea-utiful objects for examination. They 

 may be laid on a slip of glass in water, and covered 

 over with a piece of thin glass ; or they may be 

 placed in the animalcule-cage. They consist of a 

 series of cells growing end to end, and their parti- 

 tion-walls can be easily seen. They are of a green 

 colour, from the chlorophyle contained in their 

 interior. In the case of the yoke-threads, the 

 chlorophyle is frequently arranged in a spiral man- 

 ner along the interior of the filament (Fig. 11, 

 PI. 1). These yoke-threads may be often seen to 

 unite with each other, and the contents of one cell 

 are emptied into the other ; forming the spore of the 

 plant (Fig. 133, PL 5). These spores, when they 

 escape from the cell in which. they are contained, 

 move about with great rapidity. The moving 

 power of the lower plants is well seen in the divi- 

 sion of these confervse, called Oscillatorias (Fig. 12, 

 PL 1). As they lie upon the glass slide they will 

 be seen to move over each other in all directions : 

 hence their name. 



