242 THE BIOLOGY OF FLOWERING PLANTS 



with roots of other plants have been described in some 

 cases, but this has not been confirmed by all investigators. 

 In addition to the complete saprophytes one American 

 species of Pyrola, Pyrola aphylla, with little chlorophyll, is 

 a partial saprophyte. 



{d) Triuridaceas : this small family, with 3 genera and 



about 40 species, is 

 exclusively tropical. 

 All are small yellowish 

 or reddish plants with 

 scale leaves. 



{e) Burmanniaceae : 

 another small tropical 

 family, with its chief 

 centre in Borneo and 

 New Guinea, and 

 with representatives in 

 America. Most of 

 the genera are com- 

 pletely saprophytic ; 

 Burmannia has auto- 

 trophic and sapro- 

 phytic species. One 

 or two species are 

 doubtfully parasitic. 

 The family is remark- 

 able for the extra- 

 ordinary forms of its 

 flowers (Fig. 29) . 

 Some species possess 

 rhizomes which may 

 be coral-like ; others produce shoots from the roots. 



(/) Orchidaceae. This great cosmopolitan family has 

 more than 400 genera and 7000 species ; about 50 species, 

 belonging to a dozen genera, are saprophytes, some only 

 partial. It is likely that the family includes many other 

 species of partially saprophytic habits : practically all 

 harbour mycorhizal fungi. Three saprophytic species occur 



Fig. 29. — Thismia Aseroe. Nat. size. 

 (After Groom.) 



