COMPOUND ORGANISMS 197 



leguminous plant, which hitherto has been 

 paying out carbohydrate food to the bacillus, 

 now begins to receive, and the harvest is 

 a rich one, for it acquires from the degenerat- 

 ing mass of bacilli the stores of nitrogenous 

 matter they have accumulated, and this affords 

 a very good return for the sugars, etc., which 

 it had previously expended. 



The comparatively few surviving bacilli 

 serve to infect the soil, as the roots gradually 

 rot, and they thus are enabled to attack the 

 roots of new leguminous plants with which 

 they may be brought into contact. 



In comparing the leguminous plants with 

 the saprophytes and parasites that have 

 undergone simplification (or u degeneration ") 

 of vegetative structure we can readily under- 

 stand why they have not lost their green 

 leaves, and all that the possession of green 

 leaves entails. For a continuous supply of 

 carbohydrate is essential for the growth of 

 the bacilli, and without it there is no manu- 

 facture of nitrogenous substance from the 

 free nitrogen of the air. Moreover, the Legu- 

 minosae have by no means abandoned the 

 absorption of nitrates from the soil. The 

 combined nitrogen they acquire from the 

 bacilli is, for most of them at all events, 

 rather of the nature of an additional supply, 

 though it will, and often does, enable them 

 to thrive under conditions of nitrogen starva- 

 tion which would be fatal to the majority 

 of other plants. Ultimately, however, they 



