JOHNSON & STOKES 
was formerly gained, for agricultural sciences now recog- 
nizes the fact that nitrogen, the most expensive element of 
fertility, can be taken from the air and added to the plant food 
in the soil by means of certain plants which have the pecu- 
liar habit of regu- 
larly forming little 
tubercles or lumps 
on their feeding 
roots. These 
lumps are to be 
found on plants 
in perfect health, 
and are not para- 
sitical in any hos- 
tile sense. The 
lumps are rilled 
with small living 
organisms called 
bacteria, and, 
hence, have been 
called bacteroid 
tubercles. The 
minute tenants 
slowly but surely 
secrete nitrogen, 
and put it in a 
form adapted to 
^_^^$^w^^^ plant growth. 
r^>m _, -. The pl an ts 
Crimson or Scarlet Clover, a Nitrogen Gatherer. , . , , L , 
which bear these 
root lumps belong to a group called legumes, of which 
clover, peas, beans, vetches, etc., are familiar examples. 
Curiously enough, nearly all the leguminous plants are 
thus fitted by nature by means of the root lumps to act as 
