CLIMBERS, PARASITES, SAPROPHYTES. 205 



nearly so common as the plants just mentioned, and grows 

 chiefly in dry chalky pastures in the south of England. 



Examine the Mistletoe, if possible a plant growing on its host tree. 

 It is shrubby, with smooth green stem, repeatedly forked at the 

 swollen nodes. Each branch bears two opposite leathery green leaves 

 (sometimes a circle of three leaves) and represents a year's growth ; 

 the leaves are evergreen. The flowers (March-May) are in groups of 

 three or five in the forks of the branches. The fruits ripen in winter 

 and have white pulp around a single seed ; the very sticky coating of 

 the seed prevents birds from swallowing the seed, which they scrape 

 from their bill, and if this happens on a suitable tree germination occurs. 

 The radicle forms an attaching disc from which a sucker grows into the 

 wood of the host and gives off lateral roots which grow in the cortex 

 and produce further suckers into the wood. 



238. Total Saprophytes. British examples of totally 

 saprophytic flowering plants are the Bird's-nest Orchid 

 (Neottia) and the Yellow Bird's-nest (Monotropa, allied 

 to the Heather family). Both plants get their names from 

 the nest-like mass formed by their numerous clustered 

 roots, and both grow in shaded woods and plantations, 

 Neottia in Beech woods, Monotropa in woods of beech, 

 pine, and birch. Both have erect flowering shoots bearing 

 brown or yellowish scales instead of green leaves and ending 

 in a raceme of flowers. In both cases the plant can only 

 grow in soil containing abundant decaying vegetable matter 

 (humus), and is enabled to use this for its nutrition by 

 the aid of a fungus which infests its roots. Humus is 

 always permeated with the threads of fungi, and in Mono- 

 tropa these threads form a dense felted covering on the roots, 

 while in Neottia the threads enter the cortex of the root and 

 actually grow in the living cells of the cortex. 



Thus the flowering plant is supplied with digested and 

 soluble organic food which it could not absorb in the ordinary 

 way by its root-hairs from the soil. The fungus by its asso- 

 ciation with the roots also gains certain advantages, such as 

 shelter from drought, so that the arrangement is an example 

 of symbiosis, which may be denned as a mutually beneficial 

 partnership, or an association of two organisms in a common 

 life to the benefit of each. This particular kind of symbiosis 

 is called a mycorhiza, i.e. an association of a fungus with 

 the roots of a higher plant. Symbiosis must be carefully 



