Monotropaceae with Reference to Ericaceae 79 



glomerate crystals, about one-third the size of a normal mesophyll 

 cell, and as much larger masses, completely filling an enlarged 

 mesophyll cell. They are mentioned by Rommel (65) who has 

 also given a short description of the microscopic structure of 

 the leaf similar to Petersen. Both of these descriptions, how- 

 ever, deal with only the laminar portion of the leaf. 



At the midrib, the halves of the lamina form an angle of 90 , 

 and the leaf extends out into a ridge. The upper epidermis is 

 similar to that over the lamina, consisting of rectangular cells (on 

 transverse section) with thickly cuticularized walls, especially 

 on the outer surface. Beneath the upper epidermis, the palisade 

 tissue thins out to only one layer of cells, that are almost iso- 

 diametric. Immediately below this is the midrib vascular 

 bundle. Within the bundle sheath is a fan-shaped area of 

 xylem, below which is a narrower region of phloem, composed 

 of a narrow area of soft, and a wider area of hard, bast. Be- 

 neath the bundle are two layers of spongy parenchyma cells, 

 which are round, somewhat thick-walled, and closely packed 

 together. Next to this is one layer of rounded cells, pressed 

 tightly against the lower epidermis. The walls are rather 

 heavily thickened, so that in cutting they easily break away 

 from the rest of the spongy mesophyll. The lower epidermal 

 cells, at the midrib region, become less rectangular, more iso- 

 diametric than in the laminar portion, the cuticle of each cell 

 swelling out somewhat, so that the outline of the lower epidermis 

 in transverse section becomes crenulate. 



C. maculata, while showing essentially the same type of leaf 

 as C. umbellate, differs slightly in structure. The upper epi- 

 dermis consists of wavy walled cells, in surface section, appear- 

 ing rectangular in transverse section, except that the outer 

 face of each cell protrudes from the surface forming a short 

 rounded papilla. This is, however, confined to the upper epi- 

 dermis, the cuticle of the lower being perfectly flat as in C. 

 umbellata. Chloroplasts occur in both upper and lower epi- 

 dermis, no hairs are present, and stomata, similar in form to 

 those of C. umbellata, but projecting slightly from the epidermis, 

 occur on the lower surface. The palisade tissue consists of 

 but two layers of elongated cells. The spongy mesophyll has 

 several layers of irregularly branching cells with large inter- 

 cellular spaces. Both palisade and spongy mesophyll cells are 



