Ironside. — Anatomical Structure of N.Z. Piperaceae. 



343 



The petiole of P. EndUcheri shows one large central bundle and two 

 smaller ones, one on each side of the central one. The leaf shows an 

 epidermis consisting of several layers, as seen in many Peperomias. The 

 mesophyll-cells are also large, contain but very little chlorophyll, and store 

 water. 



Base, of Macropiper. 



The base of M. excels um is swollen, and stored with nutritive material 

 (fig. 6a). This is shown even in young specimens. The nutritive material 

 chiefly takes the form of starch, which is contained in the medulla and 

 medullary rays, and also in the cortex. 



In the young branch coming from the base of the stem the stem shows 

 two rings of vascular bundles, as usual. But the sclerenchyma appears 

 only on the inside of each bundle of the outer ring ; there is no continuous 

 band of sclerenchyma, though there are occasionally slight indications^of 



Fig. 6a. 



a, Base of M. excehvm (x scars where stems have been broken off) ; b, young 



seedling, half life-size. 



extension of thickening between the bundles. The more usual number 

 of bundles in the medullary circle in the youngest parts seems to be three. 

 As one passes up the stem the sclerenchymatous elements gradually form 

 a continuous band. 



Coming to the main stem, near the base in the region marked 1 in 

 fig. 6a, b, there is a distinct corky layer outside with a collenchymatous 

 band below. The structure of the rings is much the same as higher up 

 the stem, but there is abundant starch everywhere. The bends of the 

 sclerenchymatous ring, also, are here much deeper, and extend more into 

 the interior of the stem. 



As one passes down to region 2 the sclerenchymatous ring gradually 

 disappears, and sclerenchyma occurs only to the inside of each bundle, 

 extending over into the medulla in more or less club-shaped, rounded 

 masses. The discontinuity of the sclerenchyma probably allows for the 

 easy passage of food-material. Each of the central bundles is seen to be 

 formed by the fusion of a bundle, or bundles, of the outer ring with a central 

 bundle of the internode above. Fusion invariably starts at the xylem 

 end, some bundles distinctly showing two masses of xylem at each side of 

 a central line. 



