1889.] of the stem of the Cucurbitacece. 15 



ten fibro- vascular bundles in two concentric rings, the five inner 

 bundles being larger than the five outer ones (fig. 1). The stem 

 increases slowly for some time, because the cambium on the outside 

 as well as on the inside of each bundle adds xylem and phloem 

 to the bundle; the cells of the medullary rays increase radially 

 and divide. Thus far Cephalandra is similar to the herbaceous 

 members of the order. The latter, being annuals or at least not 

 requiring a continual enlargement of the stem, have no provision 

 for such increase, whilst Cephalandra being woody and perennial 

 requires means whereby its stem can continue to grow, and there- 

 fore by division of the cells of the medullary rays adjacent to the 

 bundles and contiguous to the outer cambium cells there is formed 

 an interfascicular cambium (fig. 2a). This interfascicular cambium 

 soon stretches from bundle to bundle across the medullary rays 

 (see dotted line fig. 1), and its development agrees with that of 

 normal Dicotyledons. After the completion of the ring of inter- 

 fascicular cambium, xylem is formed on the exterior of the existing 

 xylem, and phloem on the interior of the outer phloem and secondary 

 medullary rays are formed in the xylem in the normal manner 

 (Plate II. fig. 4 mr z ). The stem therefore grows in the same 

 manner as a normal Dicotyledon. The cambium which is placed 

 on the inner side of the xylem ceases to produce new elements 

 about the time the interfascicular cambium is formed, and finally 

 disappears; so that the internal phloems are left at the centre of 

 the stem and do not undergo further increase. 



The above description shews that the mode of increase of the 

 stem of Cephalandra indica corresponds exactly with that of a 

 normal Dicotyledon in which no intermediate bundles are formed, 

 inasmuch as each possesses a cambium which forms on its inside 

 xylem and medullary rays, and on its outside phloem and paren- 

 chyma. But the stem of the former differs in the primary ar- 

 rangement of the bundles in two rings and in having some phloem 

 on the central side of the xylem. It would seem therefore that 

 de Bary's* view that the two concentric rings of bundles in the 

 stem behave as a single ring curving alternately outwards and 

 inwards is correct. 



EXPLANATION OF PLATES I AND II. 



Fig. 1. Diagram shewing position and relative size of the fihro- 

 vascular- bundles of the stem of Cephalandra indica. 

 Ph = Phloem, Xy = Xylem, the wavy line indicating where 

 the interfascicular cambium will be formed. 



Comparative Anatomy, English edition, p. 45G. 



