94 Henderson — Comparative Study of Pyrolaceae and 



In the Pyrolaceae, all of the species have five distinct petals. 

 This is also true of the most primitive group of the Ericaceae, 

 namely, the Rhododendroideae-Ledeae where Elliottia has four, 

 Tripetaleia three, Cladothamnus five, Bejaria seven, and Ledum 

 five petals. Distinct petals also occur in several members of 

 the Monotropaceae, i.e., Monotropa hypopitys with 5-4, M. 

 uniflora 5-6, Pleuricospora 5-4, and Cheilotheca three. In other 

 members of the Monotropaceae the petals are united. In 

 Pterospora, the corolla is urceolate, resembling that of Andro- 

 meda. In Sarcodes and Schweinitzia it is campanulate, and in 

 Newberrya urceolate to campanulate. Urceolate and campanu- 

 late corollas are quite characteristic of many of the Ericaceae. 

 In the Ericaceae proper one can trace all transitions from a 

 flat saucer-shaped corolla with separate petals, as in Clado- 

 thamnus; to shallow campanulate, as in Loiseleuria procumbens; 

 to deep campanulate, Epigaea; to campanulate becoming slightly 

 irregular bilobed, as in Rhododendron; to urceolate in Andromeda 

 and Vaccinium; to deeply urceolate in Erica and Thibaudia. 

 In the Monotropaceae, all these stages do not occur; there is 

 quite a big gap between a corolla with distinct petals, as in 

 Monotropa, and an urceolate one as in Pterospora, or campanu- 

 late as in Sarcodes and Schweinitzia. This would point to the 

 view that perhaps these three arose from a higher group of the 

 Ericaceae, and that the others arose from the Rhododendroideae- 

 Ledeae with distinct petals. The very great similarity of these 

 to each other (particularly Sarcodes and Pterospora, the writer 

 having no good material of Schweinitzia) in all of their parts, 

 and the rather great difference in structure between them and 

 all other members of the Monotropaceae and Pyrolaceae give 

 further evidence toward this view. In Chimaphila and P. 

 rotundifolia and P. elliptica the corolla is slightly irregular — 

 one petal extends downward so as to form a resting place for 

 the insect. This parallels the condition in Rhododendron where 

 the corolla is slightly bilabiate. 



The presence of hairs on the inner surface of the petals seen in 

 Monotropa is a characteristic of many members of the Ericaceae. 



The Stamens 



In all of the Pyrolaceae, the stamens, ten in number, are 

 arranged in the bud so that the pores of the anthers point down- 

 ward. When the flower opens, the anthers tilt backward, so 



