Monotropaceae with Reference to Ericaceae 85 



equal in size pass through the mesophyll so that at the midrib 

 the scale is only slightly thicker than in the laminar region. 

 The bundle is even more reduced in size and number of ele- 

 ments than in Pterospora and Sarcodes, the woody tissue con- 

 sisting only of one to two elements, the main part of the bundle 

 being composed of phloem. 



The leaf of M. uniflora is exactly similar in structure to that 

 of M. hypopitys except that no hairs are present in M . aniflora 

 and stomata are even more rare than in M. hypopitys (Fig. 4, 1). 

 The writer found only one stoma on the lower epidermis of each 

 leaf. 



The leaf of Pleuricospora fimbriolata is very similar in its 

 structure to that of Monotropa. The epidermal cells are slightly 

 longer than wide on surface view, and oval in transverse section. 

 They are covered by a thin ridged cuticle and layer of wax. 

 No hairs or stomata are present. There are eight rows, at the 

 widest part, of thin-walled, closely packed hexagonal cells. 

 The midrib bundle is only slightly larger than the others and is 

 even more reduced than in Monotropa. 



From reviewing literature on the structure of the leaves of 

 the Ericaceae (88, 56, 60, 73) and from an examination of sec- 

 tions of the leaves of various members of the family, the writer 

 finds that in general the structure is very similar to that of 

 Chimaphila, which the writer considers to be the least sapro- 

 phytic genus of the Pyrolaceae. The Ericaceae generally agree 

 with Chimaphila in having a thick cuticle, often with a coating 

 of wax, a mesophyll differentiated into palisade and spongy 

 regions, and chlorophyll in the upper and lower epidermis. 

 Solereder reports cuticular ridges as a common occurrence in 

 the Ericaceae. Their presence has been indicated in all the 

 Pyrolaceae and Monotropaceae examined. Papillae on the 

 epidermis, except at the midrib, are rare in the Pyrolaceae and 

 Monotropaceae, only occurring in C. maculata. They are 

 present, however, on the lower epidermis of Rhododendron 

 campylocarpum, R. thomsoni, Kalmia glauca, K. latifolia. At 

 the midrib in typical Ericaceae, the epidermal cells often bulge 

 out to form papillae. This is true of Chimaphila and Pyrola 

 also. 



Stomata in the Ericaceae and Pyrolaceae may be present on 

 the lower surface only, but are frequently present on both sur- 



