260 



Science of Plant Life 



Bureau of Agriculture, P. I. 



FIG. 152. A field of young bananas, with cowpeas planted between the rows to 

 enrich the soil. 



a microscope, it will be found to be filled with bacteria. These 

 bacteria are parasites and take their food from the legume, 

 but by the processes which they carry on in the nodules, they 

 change nitrogen from the soil air into nitrogen compounds, 

 just as the soil bacteria mentioned in the preceding section 

 do. The nitrogen compounds thus formed are used by the 

 host plant, and when the latter is plowed under and decays, 

 the nitrogen compounds are made available for a succeeding 

 crop of wheat or corn. 



The fungi. The fungi form an exceedingly large and di- 

 versified group, ranging in size from microscopic forms of a 

 single cell to the large, fleshy mushrooms and to the bracket 

 fungi found on tree trunks and logs. Among the most impor- 

 tant fungi are yeasts, molds, mildews, smuts, rusts, and 

 mushrooms. We cannot here describe the many interesting 

 forms and give their life histories. They all lack chlorophyll, 



