HISTOLOGY OK OELSEMLUM SEMI'ERVIRENS. 505 



small, lying in all directions, level with the surface, each bordered with 

 5 or ii ordinary epidermis cells. Hairs of two types, about equally 

 numerous. First, long, sharp-pointed, with cuticle somewhat rough- 

 ened, composed of 2 to 4 cells in one series. Second, multicellular, 

 probably glandular, shield hairs, with a very short stalk which occu- 

 pies slight depressions in the epidermis so that the flattened, disk- 

 shaped head appears to rest on the surface; head composed of 6 to 18 

 wedge-shaped cells. 1 



Palisade in one layer. Pneumatic tissue quite compact. 



Larger veins prominent beneath, the mestome bundle or group of 

 bundles (several bundles, inclosing pith, form the midvehi), almost 

 entirely surrounded by a narrow ring of rather thin-walled steromc, 

 which is separated above and below from the finally massively devel- 

 oped hypodermal collenchyma by thin-walled, colorless parenchyma, 

 which becomes collenchymatic in old leaves. 



Gelsemium sempervirens L. 



In most different situations, from the Ilygrophile Forest to the Sand 

 Strand. 



Leaves evergreen, thickish, shining above, horizontal, bifacial. 

 (Leaves examined probably in their second season.) 



Epidermis: Ventral, cells large and liigh, the cuticle and outer wall 

 much thickened, the other walls thin, the radial not undulate. Dor- 

 sal, cells smaller, their walls thinner, and not or but slightly undulate. 

 Stomata only on the dorsal surface, lying in all directions, somewhat 

 prominent, the guard cells each accompanied by a parallel subsidiary 

 cell, with occasionally a third parallel cell of similar form. 2 Hairs, 

 none. 



Palisade, cells low and comparatively wide, only the uppermost 

 layer perfectly compact; the next two similar but with small inter- 

 cellular spaces; then about two layers of open pneumatic tissue with 

 nearly isodiametric cells; and finally a continuous layer of chloren- 

 chyma adhering to the dorsal epidermis, easily separating from the 

 pneumatic tissue, witli its cells elongated in a direction parallel to the 

 surface. 



Hypodermal collenchyma in two layers beneath the midvein, thick- 

 walled. 



1 Prillieux (Ann. Sc. Nat. Bot., ser. 4. vol. 5, p. 9, t. 2,f. 14) states that the num- 

 ber of cells is 13 and the diameter of the head is 55 micromillimeters. These fig- 

 ures can be taken as representing the average number and size, although the 

 variation is considerable. 



'-' The relation is comparable to that figured for stomata of Rabiaceae with three 

 subsidiary cells (Solereder, Syst. Anat., p. 503,/. 101, 67), except that in Gelseminin 

 all the cells are of approximately equal size. 



