62 VEGETABLE GARDENING. 



applied to the whole area intended for this crop, or 

 to special trenches where the lines of peas are to be 

 sown. After digging, apply basic slag on the surface 

 at the rate of 5 Ibs. to 30 square yards, and in spring, 

 before sowing the seeds, sulphate or muriate of 

 potash, at the rate of 2 Ibs. to 30 square yards. No 

 nitrogenous fertilisers are required for this crop in a 

 good soil. Peas and beans possess the remarkable 

 power of being able to take up and assimilate the 

 free nitrogen of the air. This they do through the 

 agency of certain bacteria (Pseudomonas radicicola) 

 which inhabit the nodules to be found on the roots. 

 The bacteria take up the free atmospheric nitrogen, 

 and manufacture it into nitrogenous compounds on 

 which the plants then feed. Such an arrangement, 

 whereby one plant or organism elaborates food for 

 another plant with which it is closely connected, is 

 called symbiosis (a " living together "). This source 

 of supply, in addition to the nitrogen obtained from 

 the soil and farmyard manure, is, as a rule, more than 

 ample for the needs of the crops. 



In this connection it may be pointed out that when 

 rows of peas and beans are being cleared away, after 

 the crop is exhausted, the plants should be cut over 

 at the surface of the ground ; the roots of these 

 plants should not be pulled up, but allowed to decay 

 naturally in the soil. The reason for this is that 

 these pod-bearers, unlike other plants, have attached 

 to their roots a quantity of small, but quite visible, 

 nodules or swellings, each containing a large number 

 of useful bacteria, along with a considerable amount 

 of valuable nitrogenous plant food which they have 

 been the means of producing. To pull these up 



