Finlayson. — Stem- structure of Leafless Plants. 365 



and polygonal in transverse section. Its cells are smaller 

 than those of the chlorophyll-containing tissue which lies on 

 either side of it. As the stem grows older its cell-walls 

 become much thickened, and the protoplasmic contents dis- 

 appear. If a transverse section of the stem (mounted in 

 water) be treated with chior- zinc-iodine, the walls of the 

 mechanical tissue, as well as those of the cuticularised outer 

 epidermal wall, are stained yellow, those of the wood-tissue 

 being stained a deeper brown. So it is probable that the 

 thickening of the cells of the mechanical tissue is of a similar 

 nature to cutin. The cells of this tissue are elongated, with 

 oblique transverse walls (fig. 5d, m. st.). 



Immediately below each strand of mechanical tissue is a 

 vascular bundle. Between the thickened elongated cells of 

 the mechanical strand and the phloem of the vascular bundle 

 are a few parenchyma cells (figs. 5b, par. c. ; 5d, par. c). 



The vascular bundle is open, consisting of phloem, 

 cambium, and xylem. It forms but a small proportion of 

 the total stem-radius, and is not modified specially to per- 

 form a mechanical function as in the stem of Discaria 

 toumatou. 



The phloem consists of phloem parenchyma, sieve-tubes, 

 (fig. 5d, s. t.), with a few bast fibres consisting of long, narrow, 

 thick-walled cells (fig. 5d, b. /.) occurring on outside of the 

 phloem tissue. 



The xylem elements include a few spiral vessels 

 (fig. 5d, sp. v.). I also saw an annular vessel (fig. 5d, a. v.) 

 on the inside, a few pitted vessels (fig. 5d, p. v.) towards 

 outside of the xylem, and a few woody cells, elongated, with 

 oblique transverse walls ; thickened parts alternate with thin 

 spaces on both longitudinal and transverse walls (fig. 5d, w. I.). 

 Between the xylem and phloem are a few cambium cells, with 

 the ordinary conspicuous nuclei and thin cell-walls. 



The stem of Clematis afoliata, like that of Discaria 

 toumatou, is entirely wanting in hairs. A certain amount 

 of protection against excessive transpiration is afforded by 

 the cuticle of the epidermis, and by the fact that the stomata 

 occur only in the depressions of the stem ; at the same time 

 the air-spaces of the chlorenchyma allow abundant aeration, 

 so that the chlorenchyma can carry out the work of assimila- 

 tion satisfactorily. The mechanical tissue is able to keep the 

 stem sufficiently stiff, so that no special development of the 

 vascular tissue is necessary. 



Cabmichaelia. 



Three species of Carmickaelia (C. flagelliformisj G. monroi, 

 and C. nana) remain to be considered. 



