252 APPLIED BIOLOGY 



Algce in Water Reservoirs. On the harmful side there is 

 very little to be said against the plants of the algae group. 

 Probably most important is the fact that certain species 

 grow extensively in reservoirs used for storing water, and 

 impart a very disagreeable odor and flavor to the water. 

 Some of the cities in eastern Massachusetts and New York 

 City have had much trouble in this line. A small amount of 

 copper sulphate dissolved in the water prevents the growth 

 of such algae ; but such chemicals must be used with caution 

 until scientific experiments demonstrate whether or not 

 small quantities in drinking water may not be harmful 

 when used continually. 



2. SPORE-PLANTS WITHOUT CHLOROPHYLL: FUNGI 



243. The most important examples of spore-plants which 

 have no chlorophyll, and hence must be in their food-sup- 

 ply different from green plants, are common molds, mush- 

 rooms, and yeast-plants. To these might be added the 

 bacteria ; but many peculiarities and their great importance 

 make it best to devote a separate section to them (beginning 

 with 254). 



Molds 



244. Study of Common Molds. It is a well-known fact 

 that when bread, cheese, or other foods are left for some time 

 in a damp place, there appears over the surface a mass of 

 delicate threads or filaments, and the bread is said to be 

 " molding " or " moldy." Soon the color of the moldy 

 mass changes from white to black, blue-green, or brown, 

 and according to the color, the names black mold, green 

 mold, and brown mold are applied. 



(L) Examine pieces of bread on which black mold is growing. 

 Break off pieces and note that delicate threads run through the 

 bread (use a hand-lens). These threads are the hyphce, and the 

 entire mass of them is the mycelium. Starting on the surface, the 



