i9o8.] OF THE SAND DUNE PLANTS OF BERMUDA. 103 



Staurophyll. — Hcliotropinm cnrassazncujii, Conocarpns crcctus 

 (thick leaf), Sccevola Plumieri, Tournefortia gnaphalodcs- ^ 4. 



Spong-ophyll. — Sisyrinchium hernmdiamim, Stenotaphrum ameri- 

 cannm, = 2. With reference to the last two plants, it should be 

 mentioned that the leaves of these plants stand erect, thus receiving 

 the incident rays of light on the edge of the leaf, hence the absence 

 of palisade tissue and the presence of spongophyll structure. 



Detailed Structure of Leaves. — The sections of the leaves 

 which were studied were made free-hand with a razor. After stain- 

 ing, the sections were mounted for permanency in Canada balsam. 

 The drawings of these sections were made by the use of the micro- 

 projection, electric lantern, so that in every case with the exception 

 of Croton maritiiints, the drawings were made on the same scale. 

 The sketches of stomata are none of them drawn to the same scale. 

 The description of the histologic structure of the leaves of each 

 species follows. 



Passiflora suberosa is a small, slender species of the genus found 

 growing over the sand surface of the dunes in the parish of Paget. 

 Its flowers are small and the branch tendrils are characteristically 

 developed. Histologically the leaf presents an upper epidermis of 

 large thin-walled cells, and as the whole plant is brilliantly illumi- 

 nated, it has two well-marked layers of palisade cells. The loose 

 parenchyma is narrow and some of the cells of it are filled with con- 

 glomerate crystals. The stomata are slightly raised above the gen- 

 eral epidermal surface, and are confined to the lower side of the 

 leaf. A diphotophyll (Fig. i, Plate II.). 



Canai'alia obtusifolia, a trailing leguminous plant, has paripinnate 

 compound leaves with a long petiole and broadly elliptical leaflets 

 with retuse apices and petiolules, a quarter of an inch long. The 

 upper epidermis consists of slightly thickened cells. There are two 

 rows of palisade cells, a considerable amount of loose parenchyma, 

 while the slightly raised stomata are found on the upper and under 

 sides. The adaptation to the environment of the sand dunes seems 

 to be the folding together of the two sides of the leaves along the 

 midrib, so that the edges of the leaves are presented to the incident 

 rays of light. A diphotophyll (Fig. 2, Plate II.). 



Euphorbia biixifolia is a prostrate, tufted plant of a rosette habit. 



