70 SAPROPHYTIC PLANTS [CHAP. 



the effect of producing such degradations of 

 structure as are found in the foliage of colour- 

 less parasites ; rather, indeed, the reverse ; for 

 if, e.g., wheat has its leaves of a deep rich 

 green colour, this signifies that it is consuming 

 too much nitrogen from the soil. Greenless 

 saprophytes, therefore, were perhaps in some 

 cases at first parasites, their parasitic habit being 

 changed to one of saprophytism, their degraded 

 structures being retained. 



In tropical forests, however, where there is 

 ever-forming decayed vegetation, and the greater 

 number of saprophytes exist, the darkness pre- 

 vailing is probably the primary influence, which 

 induces etiolation in germinating plants which 

 have "taken to" saprophytism in self-preserva- 

 tion in the struggle for life. 



Although this would seem probably to have 

 been the case, it does not preclude the possi- 

 bility of an ordinary green plant becoming 

 saprophytic. As a case in point, a species of 

 fern (Gramatophyllum) has been known to 

 produce its aerial roots among decayed vegetable 

 matter. In this case, on a careful examination, 

 I found that the surface of the roots in contact 

 with it had developed quantities of "absorbent 

 hairs." These were doubtless induced to be 

 formed by the presence of nutritive matter. 1 



As another case, I found that the rhizomes 



1 Journal of the Royal Horticultural Society, vol. xvi., p. xxiii., 1893. 



