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 “ 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- 
minosze 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 
