VERBENA CILIATA. II 



VERBENA CILIATA* BENTH. 



Verbena ciliata (plate 3) is a plant with showy flowers which may persist 

 by means of its roots and by half -withered stems through a rather extended 

 period of drought. Though an annual in type, it therefore often becomes 

 perennial. 



The leaves (130 micra in thickness) are of a common mesophytic bifacial 

 type, with an arrangement of chlorenchymatous tissues very similar to 

 that in Raphanus (Haberlandt, Physiologische Pflanzenanatomie, p. 256). 

 This is characterized by a 3 -layered palisade tissue. The epidermal cells 

 are of the very generally distributed type, with wavy outlines, and both the 

 epidermis and cuticle are thin (plate 13, fig. i ; plate 7). 



Both surfaces of the leaf have bristle and glandular hairs, which stand in 

 such scattered positions that they can scarcely be interpreted as mechanical 

 suppressors of water loss. They are more abundant on the lower surf ace. The 



stomata are, like those of 

 the ocotillo, of a simple 

 type, with a very slight 

 inner ridge (fig. 4). The 

 secondary thickening of 

 the guard-cell wall affects 

 chiefly the lower wall. 

 The hinge which, in oco- 

 tillo, is replaced by a thin- 

 ner line of wall in the 



FIG. 4. Stoma of Verbena ciliata in transverse section. 



adjacent epidermal cell, is 



quite marked in Verbena. The form of the pore at various degrees of expan- 

 sion is shown in the diagrams in fig. 5, drawn to the same scale. The widest 

 opening is 10 micra in width and 15 in length. It will be observed that the 

 transverse form of the pore is materially changed after a width of 6 micra 

 has been obtained, and that the geometrical figure departs from the closer 

 approach to the elliptical taken by the pore when it is less than 6 micra in 

 width. These figures, and the similar ones already given of the stomata of 

 Fouquieria, are of much interest, as they suggest a method for the exten- 

 sion of the field of study so ably opened up by Schwendener, in which the 

 methods employed in the work to follow may be of very great aid in pushing 

 the mechanical analysis of stomatal movement to a high degree of refinement. 

 The relation of this change of form to the diffusion capacity of the opening 

 will be referred to later. 



In addition to starch there is present, at times, a droplet of oil in each 

 guard-cell. The amount of oil and of starch is subject to certain fluctuations, 

 which will be considered at length beyond. 



*Benth: Plantae Harthw.. 21. 



