250 



ELEMENTARY SCIENCE 



fastened to rocks or floating in the water when you have 

 been in wading. These threads are one cell in thickness, 

 but many cells in length, as may be seen under a micro- 

 scope. In some of these cells many small bodies are found. 

 These little things escape into the water where they swim 

 around. They seem like little animals they are so active. 

 Sometimes two of these little things unite. After they unite, 

 they stop moving. They have formed a single cell, and 

 this cell presently will grow into a 

 row of cells (see Fig. 90). This 

 production of a new individual as a 

 result of the union of two cells is the 

 sex process, or reproduction, and 

 we are going to see what this proc- 

 ess has to do with the production 

 of seeds. 



Now you have seen two steps in 

 the story of seeds. First, the little 

 plant that reproduces simply by 

 dividing. Next, the little plant 

 that reproduces by the union of 

 two cells. Now if these two cells 

 that unite are of different sizes (as is true of most plants), 

 we call the smaller one the sperm and the larger one the egg. 

 This is important to remember, for all the higher plants 

 and animals reproduce by means of sperms and eggs. 



If you have ever been at the seashore you have been 

 interested in the tides. Have you ever noticed the plants 

 that lie on the mud at low tide ? Probably the first plants 

 that ever lived on land were plants that were left behind 

 on the mud by the receding tides. Of course the greatest 

 danger to a plant is the danger of drying up. All land- 



FIG. oo. One of the algae, show- 

 ing how the small reproduc- 

 tive bodies are formed within 

 the cells; how they break 

 loose and swim about (c) ; how 

 they pair (d ) and form a single 

 cell (e), "which grows into a 

 new individual (D). After 

 J. M. COULTER. 



