170 



FRIENDS AND ENEMIES OF PLANTS 



of peaches, apples, etc. They are readily passed from one plant or 

 animal to another. 



Agents of Nitrification. The bacteria in the soil are the chief 

 means of making nitrogen available to plants. One kind seem to 

 have the power of taking the free nitrogen in the soil air and fixing 

 it in the form of solid compounds. Another kind gather nitrogen 

 from the air through their relation to the roots of certain kinds of 



plants known as legumes or 

 nitrogen-gatherers such as al- 

 falfa, clover, peas, beans, and 

 the like. The nitrogen is 

 stored in tubercles on the 

 roots. 



Yeast. We have all learned 

 something about yeast from 

 observing its use in making 

 bread, but, perhaps, if we were 

 called upon to say whether 

 yeasts were plants or animals 

 we should hardly know what 

 opinion to express. Upon 

 close examination we find 

 that yeasts are one-celled 

 plants which play an impor- 

 tant part in certain kinds of fermentation employed in the making 

 of bread and in the manufacture of beer, wine, and spirits of various 

 kinds. In this process the sugar is broken up into alcohol and 

 carbon dioxide. The latter, expanding under the influence of 

 heat, puffs up the pores of the dough and makes it rise. Were it 

 not for the action of this gas our bread would be heavy and unfit 

 to eat. These same little plants acting on the sugar in cider and 

 sweet wine set up fermentation and cause them to sour. If we 

 place a little yeast in sweetened water, in a little while we notice 

 bubbles of gas escaping; and if this be collected and tested, we 

 find that it is carbon dioxide. Yeast plants reproduce themselves 

 by budding. 



Fungous Diseases. The various diseases caused by the 

 presence of fungi are usually designated as fungous diseases. 



Nodules on roots of red clover. 



