PHOTOPHYTES. 4.3 



as green fibers or threads in almost every running 

 stream. The microscope will show the cells of these 

 fibers applied end to end the cells at each end mul- 

 tiplying by self-division. In another kind, adjacent 

 cells grow together, and the green chlorophyll and 

 bioplasm mix in one of the cells, forming a sort of 

 spore, or seed, which produces a new filament by cell- 

 division. (Fig. 16.) 



4. The unicellular plants most interesting to those 

 who study with the microscope are called Diatoms, 

 (from two Greek words signifying to cut through,) 

 because of the ease with which a chain of them may 

 be broken up into individual cells. These cells con- 

 tain chlorophyll, generally of a brownish color, and 

 the external membrane, or cell- wall, is hardened by a 

 deposit of flinty matter. There are many kinds of 

 Diatoms, with flinty shells, beautifully marked with 

 lines and dots, often surpassing the most complicate 

 patterns of art. Some are globular in shape, some 

 flat with sides like a pill-box, others square, triangu- 

 lar, boat-shaped, etc. They move about in the water, 

 so that some have thought them to be animals. Many 

 are so minute as to require the very finest micro- 

 scope to make out their details. Each cell consists of 

 two valves, or plates, applied together like the valves 

 in a muscle-shell. Fig. 17 shows a valve of one of 

 the most ornamental diatoms the Arachnoidiscus 

 Elirenlergii. The first of these words signifies a disk 



