ORIGIN OF SAPROPHYTISM 243 



in Britain ; Corallorhiza innata, the coral-root, and the much 

 rarer Epipogon aphyllum are devoid of roots, possessing 

 coralloid rhizomes ; Neottia Nidus-avis, the bird's-nest 

 orchis, possesses roots. These plants are brown or yellowish 

 in colour, though Neottia possesses some chlorophyll, and 

 have leaves reduced to scales. Epipogon and Neottia occur 

 in shady woods in rich humus soil ; Corallorhiza is peculiar 

 in inhabiting sandy copses. 



General Remarks. — As has been said, all saprophytes 

 are mycotrophic ; this habit is, as we shall see, extremely 

 widespread, and, in conjunction with gro^vth in rich humus 

 soils, would seem to offer admirable opportunities for a 

 dependent existence. Yet complete saprophytes are few 

 in number. 



A good deal of work has been done in investigating the 

 possibility of normal plants absorbing organic substances 

 from the soil. It is certain that the normal root system may 

 absorb soluble organic substances like sugars. Robbins 



(1922) has recently shown that amputated root tips of the 

 maize may grow vigorously and branch on organic culture 

 media. Complete plants supplied with sugar show increased 

 growth and also increased chlorophyll content. Brannon 



(1923) has grown various plants in the dark on glucose and 

 other sugars and for periods of many weeks. Increase in 

 dry weight took place, and peas even produced flower buds. 

 This tells distinctly against any idea that chance absorption 

 of organic substance might have led to loss of chlorophyll 

 and further reduction. The fact is established that humus 

 compounds are not available for higher plants, and this 

 makes it all the more likely that the saprophytes draw on 

 the soil only through their symbiotic fungi. They must have 

 been derived from green mycotrophic plants. They have 

 originated, as have the parasites, in widely different regions 

 of the system of flowering plants. Of the causes which have 

 led to diminution of chlorophyll and further reduction we 

 know nothing, except that in ordinary plants mutations 

 with little or no chlorophyll occasionally occur, e.g. in 

 Lychnis dioica. In such mutations in plants with advanced 



