364 Transactions. — Botany. 



base. The length of a fully grown petiole is about 4 in. 



( fi g- 4 )- 



The stem is fairly slender, finely striated longitudinally ; 



when young it is very soft and flexible ; later it becomes 



firmer, but retains its suppleness. The petioles may act as 



tendrils as well as assimilatory organs. 



Internal Structure of the Stem. 



This stem bears a stronger resemblance to the ordinary 

 dicotyledonous type of stem than does Discaria toumatou. 

 In the centre is the pith of large thin-walled cells, surrounded 

 by a ring of vascular bundles with medullary rays between 

 them. The fundamental tissue shows most deviation ; it is 

 differentiated into chlorenchyma and mechanical supporting 

 tissue, which alternate round the stem. The outline of the 

 stem (in transverse section) is wavy, with alternating ridges 

 and depressions ; the ridges occur above the stereom bands, 

 the chlorenchyma occurring just underneath the depressions 

 (hence the longitudinally striated appearance of the stem). 

 There is a similar arrangement of the tissues seen also in the 

 petiole, hence only the stem-structure is described. 



Stem. 



On the outside of the stem is a 2-layered epidermis 

 (figs. 5a, 5b, 5c). The cells of the outer layer are larger than 

 those of the inner layer, which also differ in being slightly 

 elongated in a direction at right angles to the radial direction. 

 The cells of the outer layer are slightly elongated in the 

 radial direction ; on their outer walls is a firm but not very 

 thick cuticle. Stomata only occur in the depressions of the 

 stem (figs. 5a, 5b). 



The chlorenchyma cells are large, with air-spaces between 

 them. They have their longitudinal axis parallel to stem- 

 radius. They are irregular in shape, with chlorophyll 

 granules arranged chiefly on their side walls. 



Immediately under a chlorophyll strand, in a radial direc- 

 tion towards centre of stem, comes a medullary ray. The 

 cells of the medullary ray are slightly elongated, and contain 

 starch. In transverse section they appear polygonal from 

 mutual pressure (fig. 5b, m. r.). There is no formation of 

 interfascicular cambium. 



The pith is very well developed in this stem, occupying 

 about one-third of the stem-radius. It is composed of thin- 

 walled cells, larger towards the centre of the stem ; rounded 

 in transverse section, slightly elongated in longitudinal section 

 (fig. 5c). 



The mechanical supporting tissue in the young stem is 

 composed of thin-walled living-cells tightly packed together, 



