RELATION OF SAPROPHYTES TO THEIR NUTRIENT SUBSTRATUM. 115 
underground stem, peculiarly suitable for absorption, is encountered, it is regularly 
embraced by the suction cells, and as great an absorbent surface as possible is thus 
brought into contact with the nutritious fragment. Indeed, the development of 
suction cells on the roots of many gentians (viz. Gentiana ciliata, G. germanica, @. 
Austriaca, and G. Rhetica) is confined to the parts of the root-branches, which, in 
the course of their passage through the vegetable mould, have come into contact 
with a particularly nutritious portion of it. Wherever there is contact, the root is 
thickened, and absorption cells project unilaterally from the epidermis and grow 
into the decaying fragment of wood or bark which is to be drained of its nutrient 
Fig. 16.—Transverse section through absorption-roots of Saprophytes. 
1 Gentiana Rhetica. 3 The Bird's Nest Orchis (Neottia Nidus-avis). 
material (see fig. 161). Roots of this kind remind one of the root-structures of 
parasites which are furnished with so-called “haustoria”, and which will be 
discussed more in detail in subsequent pages. But they are different in that they 
absorb food not from living but from decaying parts of the nutrient substratum. 
Most plants that grow on the vegetable mould of alpine meadows, and the black 
earth deposited by snow-drifts in mountainous regions, develop flat instead of 
tubular epidermal cells as suction cells, and in this resemble marsh-plants. In 
many of these cases the roots are so abundantly and minutely ramified that they 
form a plexus investing the humus. This is likewise true of the absorptive cells on 
the rhizoids of mosses. 
Plants which lie flat against the bark of trees and have no connection with the 
ground, so that they are unable to derive nutriment from it, have a very peculiar 
method of maintaining themselves. Their roots, rhizoids, or hyphe, as the case may 
be, either grow straight into the bark or are merely adnate to its surface. In 
the latter case they are exposed on one side to the open air, and form more or 
less projecting lines and ridges ramifying in all directions, often constituting a 
regular trellis-work cemented to the bark. Sometimes, too, they are represented 
