Monotropaceae with Reference to Ericaceae 105 



cospora where the placentae are placed close against the walls 

 and the ovary is practically one-celled. At the base, however, 

 even in this most simplified form, the ovary is four-celled. At 

 the base of the ovary in practically all of the Ericaceae, there 

 is a nectariferous disc. This is represented either as a collar- 

 like rim in Chimaphila, or ten very small swellings as in P. 

 secunda, P. chlorantha, P. aphylla, and Sarcodes or ten downward 

 directed nectaries in Allotropa, Schweinitzia, Newberrya, and 

 Monotropa. The ovules in all three families are anatropous. 

 In the Ericaceae, the seeds are small with abundant endosperm 

 and a well-formed embryo; reduced in size but increased in 

 number in the Pyrolaceae with a less developed endosperm 

 with larger and fewer cells, and a formless embryo composed of 

 about 25-30 cells; still further reduced and more numerous in 

 the Monotropaceae with an endosperm consisting of a few large 

 cells and a very small embryo composed of 9-5 cells. The 

 change in the ovary from five-celled with central placentae to 

 one-celled (nearly so in Pleuricospora) with parietal placentae; 

 and the increase in number of seeds and reduction in number 

 of cells of the endosperm and embryo are all evidence of increas- 

 ing saprophytism. 



Conclusions 



From the preceding summary, it is seen that all of the sup- 

 posed differences between the Ericaceae and the Pyrolaceae 

 are broken down, except that the ovary is completely five-celled 

 in the Ericaceae, and incompletely five-celled in the Pyrolaceae. 

 The distinction is so slight that it seems unreasonable to use 

 it as a basis for separating the two families. The only dis- 

 tinction that holds between the Pyrolaceae and the Mono- 

 tropaceae is the absence of green coloring matter in the latter. 

 In M. hypopitys, small grains are present in the epidermis of 

 the scales. These are probably chromoplasts which develop 

 from chloroplasts by degeneration. 



The Pyrolaceae and Monotropaceae therefore differ from 

 the Ericaceae only in their gradually increasing saprophytism 

 and in those characters which go hand in hand with this, i.e., 

 the loss of green coloring matter, the reduction from shrubs 

 to herbs, reduction of leaves to scales, the ovary from five- 

 celled with central placentae to almost completely one-celled 



