LEGUMINOS^ 



35 



obstructing the process of evaporation which is so essential for 



their growth. 



(c) When the heat of the sun is great so as to cause more 



water to be evaporated than . the roots can absorb, the leaves 



are also seen to assume their 

 ''sleeping" attitude. As they 

 place themselves parallel to 



/ / 



Fig. 32.— Root of Gram 

 with nodules or tubercles 



(natural size). 

 C. Cell of a tubercle filled 

 with innumerable bacteria 



(120 times enlarged). 

 B. Bacteria (800 times enlarged). 



Fig 33. — Solar rays falling ver- 

 tically on a d, but slanting on 

 a c, which are both of the 

 same length. 



the sun's rays, they are 

 struck only by a few of 

 them and at oblique angles 

 (tig. 33) ; consequently they 

 do not get so hot as would 

 be the case, if they were at right angles to them. This is an- 

 other remarkable protective arrangement. 



4. The Gram plant gathering Nitrogen from the Air. — If you 

 carefully pull a Gram plant out of the soil, you will notice numer- 

 ous nodules on the roots (fig. 32) which are not accidental, but 

 have their own little functions in the great household of Nature. 

 In each little grain of earth there are numerous minute germs, 

 called bacteria. Some of these have the peculiarity of settling 



