108 HARSHBERGER— COMPARATIVE LEAF STRUCTURE [April 24, 



has smooth, thick, succulent leaves, the other has thinner, densely 

 tomentose leaves, the Borrichia frutcscens of the Southern States. 

 The succulent, smooth-leaved form has both thick upper and lower 

 epidermal cells, with the stomata on both sides, but more plentiful 

 on the lower side. The stomata are partly sunken. The palisade 

 layers on both sides are wide, but are broken into more or less ex- 

 tended patches by round parenchyma cells, which reach to the epi- 

 dermis. The loose parenchyma cells form a wide central area. A 

 diplophyll (Fig. 15, Plate III.). What the thin leaf lacks in suc- 

 culency, it gains in hairiness. Both sides are densely covered with 

 straight unicellular hairs. The palisade layers are only two in 

 number on both sides of the leaf, and the loose parenchyma is also 

 much reduced in amount. The succulency of the thick leaf fits it 

 as perfectly as the hairiness of the thin leaf to the trying seaside 

 environment, where the plants producing them grow side by side. 

 A diplophyll (Fig. is A, Plate III.). 



Croton maritimus. — The leaves of this plant studied by Kearney' 

 are bifacial, both surfaces densely covered with gray scale-like pubes- 

 cence, owing to presence of multicellular, stalked, stellate hairs that 

 cover them. The upper and lower epidermal cells have thick walls 

 and the stomata are not sunken. The palisade tissue in both the 

 upper and the lower sides are two cell layers in width with a few 

 sclerotic idioblasts. The leaf in the plant grown in the United States, 

 as depicted by Kearney, has only one row of palisade cells. Large 

 conglomerate crystals of calcium oxalate are found in the cells of 

 the loose parenchyma. Glandular capitate hairs are found on both 

 leaf surfaces. A diplophyll (Fig. 16, Plate III.). 



Totirnefortia gnaphalodes. — The leaves and stems of this plant, 

 as well as the calices of the flowers, are covered with a dense, closely 

 appressed, grayish tomentum, resembling that on our common An- 

 tcnnaria plantaginifolia and edelweiss, Leontopodium alpinum. In 

 section the hairs are unicellular, straight and of epidermal origin. 

 The palisade is formed on the upper and lower leaf surfaces and is 

 two cells thick. The loose parenchyma, occupying the center of the 

 leaf, suggests an arrangement in direction parallel to the long axis 



^ Kearney, Thomas H. " Plants of Ocracoke Island," Contributions from 

 the United States National Herbarium V : 296. 



