30 BOYS AND GIRLS IN BIOLOGY. 



made for them. Let us see if either of the hoys 

 guessed the truth. 



You probably have no trough in which you can find 

 this mould; but there is plenty. of it on old palings, 

 stone-walls, and trunks of trees. That which grows 

 on the top of old rain-water is a little different, and I 

 will tell you of this difference by-and-by. Carefully 

 scrape off a little of this mud or mould, and look at 

 it under the microscope. You will find little bodies 

 which look something like the yeast-plants — toeulje; 

 but you will see at once one great difference — these have 

 color. Some are green, some are red, and others are 

 red in the middle and green at the border (Figs. 17-20). 



Fto. 17. Fig. 18. Fig. 19. Fig. 20. 



Mould-Cell. Geeen Mould- Mould-Cell with Eed Centre and 



Cell. Eed Centee. Geeen Boedee. 



You will notice that this coloring is all inside the bag, 

 and not in the wall of the bag itself, and sometimes, not 

 often, you can see it in the form of little grains. Some 

 of these bags or cells are about the size of the yeast- 

 plants, most of them are much larger, and nearly all of 

 them have a round shape. The cell is made quite like 



