Plant Life 



Others of these minute plants are as useful as some are 

 harmful. When the housekeeper is mixing " sponge " for 

 bread, she is putting in as she stirs germs known as yeast plants 

 which abound in the air. If the sponge is set in a warm place, 

 the moisture causes them to grow 

 rapidly. The growth changes a part 

 of the starch of the flour into alcohol 

 and carbonic acid gas, which, rising 

 in bubbles, makes the bread light. 

 A sudden chill prevents their growth, 

 and the bread is heavy. Some germs 

 are necessary to cause milk to be- 

 come sour. 



Flies should be kept from dwell- 

 ing-houses and their breeding places 

 destroyed, for it has been found that 

 they spread disease by the germs 

 they carry on their feet. Sometimes 

 a germ attacks a fly. It grows and 

 multiplies rapidly, and before the day 

 is over it completely fills the fly and 

 sends out little sticky threads, which 

 fasten it to the wall or window. You 

 may often see them in wet weather. 



Fig. 2. — Fungus-filaments from 



a rotten potato. (From FiG. 3-— F^Y killed by mould. (From 



Thom^ and Bennett's "Struc- Thom^ and Bennett's " Structural and 



tural and Physiological Bo- Physiological Botany ". ) 

 tany ". ) 



Upon these threads little bodies — spores — are borne, which 

 blow about and attack other flies. Some serve locusts and 

 grasshoppers in a similar manner. It would be a good way of 

 getting rid of these plagues were it not that, for these spores 



I * 



