194 PRACTICAL LESSONS IN SCIENCE. 



These bodies sink to the bottom of the water, when released 

 by the decay of the old cells, resting there till the next season. 

 With the warmth of spring, the zygospore becomes active, little 

 bubbles of gas are formed, which float it to the surface of the 

 water, the central portion lengthens, partitions are developed 

 forming cells, which multiplying by division extend intoahairlike 

 filament. Some idea of the cell markings and of the fruiting 

 stage can be gained by examination with the naked eye or with 

 the simple magnifier, but these plants are interesting if we can 

 do no more than observe the different stages of growth, the 

 changes in color, the rapid increase in bulk, their complete disap- 

 pearance at the end of the growing season and other phenomena 

 visible to the naked eye. 



Another interesting plant colony common in ponds and sluggish 

 streams is the Water net. It is a tubular net composed of elon- 

 gated cells which, when full grown, are sometimes one-third of an 

 inch in length. The protoplasm of some of these cells breaks up 

 into a great number of daughter-cells which arrange themselves 

 into a miniature net inside the mother-cell which is set free by the 

 absorption of the enclosing walls. In other cells thousands of 

 little ciliated swarm spores are formed, which, after swimming 

 about for a time, thicken their walls and sink to the bottom of 

 the water, where they remain for a time in a resting stage, as in 

 the case of spirogyra. 



The Fungi or Moulds are closely akin to the plants just consid- 

 ered. A common one forms a greenish coating upon bread, leather 

 and other substances left in damp places. When examined the 

 green color seems to be due to a fine powder which is apparently 

 the same as the torulae. Each of these grains or spores gives 

 rise to a long tubular filament called a hypha,, and a number of 

 these hyphae, make up the body of the fungus, which is called the 

 mycelium, hyphae projecting downward and upward like roots 

 and shoots from the mycelium. Some of the hyphae projecting 

 upward develop spores at their summit. 



Moulds are easily grown for observation. A little moistened 

 horse dung placed in a, dish and covered with a glass will furnish 



