THE MONOCOTYLEDOXES 



2093 



adequate treatment elsewhere. It is, however, important to remember these 

 matters in assessing the high degree of specialization exhibited by the group. 

 When we have described, as we shall do below, the remarkable pollination 



Fig. 2029. — Orchid seedlings. A and B, Development of the first leaves from the tuberous 

 protocorm. C and D, Young protocorms about natural size. E, Section of an older 

 seedling with established plumular growth. Vascular ti.ssue in black. In the above the 

 areas of mycorrhizal infection are indicated by dotted lines. F, Section of a protocorm 

 embryo showing the entry and degeneration of the mycorrhizal fungus. Below is the 

 remains of the embryonal suspensor. On the right, three rhizoidal hairs. {After 

 Bernard.) 



mechanisms evolved (see also p. 1341), it becomes increasingly clear that the 

 Orchids must be looked on as not only a highly specialized group of plants 

 but as the highest expression of the evolution of the Monocotyledons. 



The classification of the Orchidaceae presents many difficulties, not 

 least b?ing the fact that many species and even genera are verv incom- 

 pletely known. As more facts are gathered the scheme of classification has 

 become modified until taxonomists are increasingly reluctant to formulate 

 any complete scheme. It is not without significance that Hutchinson, 

 though he has subjected the classification of all other families of the Angio- 

 sperms to close scrutiny and has made many alterations, asserts that with- 

 out a lifelong study of this family it would be unwise for him to express any 

 views. 



The scheme adopted here is that published by Schlechter in 1926 and 

 is the latest attempt to arrange the tribes in a reasonable classification. 



I. Diandrae 



There are two stamens representing the two lateral ones of the inner 



