86 Henderson — Comparative Study of Pyrolaceae and 



faces. They do not, except in a few cases, have any specially 

 formed subsidiary cells but according to Breitfeld (88) they often 

 extend beyond the surface so that they overlap the surrounding 

 epidermal cells to some extent. This arrangement is also true 

 of those of the Pyrolaceae and Monotropaceae (Fig. 4). 



The types of hairs present in Ericaceae are varied; Breitfeld 

 (88, p. 329, PI. VI), Neidenzu (56, p. 141, Pis. Ill, IV, V, 

 VI), and Solereder (73, p. 484, 485) have given detailed de- 

 scriptions and numerous figures of those found in all groups 

 of the Ericaceae. The forms of hairs present in the Pyrolaceae 

 and Monotropaceae are not numerous; in fact, hairs are absent 

 entirely on the leaves of all the Pyrolaceae. In Pterospora 

 there are present on the margin of the leaves, stalked glands 

 composed of a multiserrate stalk and a glandular head formed 

 of several cells. This type, according to Solereder, is present 

 in Arbutus, Arctostaphylos alpina, A. tomentosa, Enkianthus, 

 Gauliheria myrsinites, and G. hispida. In Sarcodes stalked 

 glands on the margin and also on the lower surface of the upper 

 leaves are very similar in structure to those of Pterospora, ex- 

 cept that in Sarcodes the glandular head is not as enlarged as 

 in Pterospora. In Monotropa hypopitys another type of hair 

 occurs. It is unicellular, short, blunt, and the waxy covering 

 is somewhat warted. This simple type is common throughout 

 the Ericaceae. 



Chlorophyll grains occur in the epidermis of many plants 

 belonging to the Ericaceae and the Pyrolaceae. Petersen re- 

 ports their presence in the upper epidermis of the leaf of Rhodo- 

 dendron lapponicum, the lower epidermis of Vaccinium vitis- 

 idaea f. pumila, upper and lower epidermis of Vaccinium oxy- 

 coccus, and states that Lidforss (45) reports their presence in 

 the upper epidermis of Ledum palustre, Loiseleuria procumbens, 

 Phyllodoce coerulea, Andromeda polifolia, Lyonia calyculuta, and 

 in both upper and lower epidermis of Arctostaphylos uva-ursi 

 and A. alpina. In the Pyrolaceae, Petersen reports their 

 presence in the lower epidermal cells of the leaf of P. rotundi- 

 folia var. grandiflora, and P. minor, in both upper and lower 

 epidermal cells of P. secunda, P. uniflora, C. umbellata, and the 

 writer has noted their presence in both upper and lower epi- 

 dermal cells of P. elliptica and C. maculata. 



The palisade tissue varies in Ericaceae from five to six layers 

 in Rhododendron lapponicum, Vaccinium vitis-idaea and Ledum 



