Monotropaceae with Reference to Ericaceae 83 



elongated cells forming a palisade of one layer. The spongy 

 mesophyll cells branch irregularly and have large intercellular 

 spaces. Starch occurs in all the mesophyll cells. Rommel 

 does not mention the presence of the one layer of palisade tissue. 

 He also states that crystals are not present, while the writer 

 finds that they are present. At the midrib the upper surface 

 of the leaf is curved slightly upward, the lower flat. Both 

 upper and lower epidermis are similar in appearance to that 

 over the lamina. The palisade cells become somewhat shorter. 

 One layer of rounded mesophyll cells occurs between the palisade 

 and the bundle. The midrib bundle is much smaller in extent 

 than in either Chimaphila or Pyrola, the latter bundles being 

 almost equal in size to the midrib. It consists of a small area 

 of xylem — not radiating as in the others — beneath which are 

 several layers of phloem. Beneath the bundle are two layers 

 of spongy mesophyll cells between it and the epidermis. 



MacDougal (48) has described in part the structure of the 

 leaf of Pterospora andromedea. He describes marginal stalked 

 glands similar to those on the flowering axis. According to him 

 "The basal scales are flecked with irregular patches of yellowish 

 brown areas, due to the penetration of the epidermal cells by 

 brownish hyphae, which completely fill them and extend over 

 the surface of the scales in a network." In a few scales the 

 writer has seen ramifying hyphae over the surface, but not 

 penetrating the epidermal cells. The epidermis consists of 

 elongated narrow cells that appear narrowly oval on transverse 

 section. Stomata, though not numerous, are present on the 

 lower epidermis. Hairs are present on the lower surface toward 

 the sides of the scale. These are simple unicellular protuber- 

 ances. The lowermost scales are smooth. Further up the 

 stalk, the scales become more and more hairy until those sub- 

 tending the flowers have long stalked glandular hairs similar 

 to the marginal ones. These consist of a rather long multi- 

 cellular stalk with an oval head composed of glandular cells. 

 The mesophyll is composed of numerous layers of thin-walled 

 hexagonal cells. The transverse section is wider at the mid- 

 rib, the midrib bundle being larger than the others. There is 

 a slight curving upward at the midrib region as in Moneses 

 uniflora. The bundles are more reduced than in Moneses uni- 

 flora. There are several xylem elements present, but the main 

 part of the bundle consists of phloem. 



