MOEPHOLOGT AND ANATOMY OF THE NYMPH.i:ACE.E. 295 



appearing perfectly collateral. However, at the point where the root first obtains its 

 individual cortex, groups of small xylem elements are seen lying between the pliloenis, 

 and at the same time the xylem underlying the phloems disappears, so tliat at this point 

 the typical root-cylinder is established. In Nf/mphcpa, where tlie roots are fewer to each 

 cluster, the root-bearing stele is smaller and more irreguhir than in Victoria, it is also 

 considerably shorter. It runs at first almost horizontally outwards, and does not turn 

 upwards until it has given off the first, i. e. lowest root. The pedicels here attain the 

 appearance of a normal root cylinder shortly after they leave the root-bearing stele and 

 before they possess individual cortices. In perfection of structure the stele formed by 

 the root-bearing bundles varies with the species. Thus, in Ni/mphcea alba and 

 N. tuberosa the 10-12 vascular bundles are arranged throughout their course in a 

 complete and w^ell-formed stele, essentially similar in all points to that of Victoria regiu. 

 In N.flava the stele is much smaller, containing al)out 6 or 7 bundles only, and it is at 

 the same time to a certain extent incomplete, for the phloem groups are very scanty or 

 altogether wanting on the inner side, especially in the lower portion of the stele. In 

 N. blanda a stele, as such, can scarcely be said to exist at all, the several root-bearing 

 bundles pass out from the central mass distinct and separate from each other. They 

 become arranged in a semicircle, and later fuse up laterally to form a continuous arc, 

 finally to form a more or less imperfect stele as in N. flava. In this respect Nymphoin 

 blanda makes a close approach to the condition observed in the Nuphars {N. advena and 

 N. hiteum), where the root-bearing bundles, some 10 in number, also pass out from the 

 central vascular mass separately, and very soon tuse together into an irregular band or 

 arc of greater or less curvature, sometimes almost a complete circle. A segment of this 

 arc becomes separated off to supply the first or lowest root ; the ends of this smaller arc 

 immediatelv grow round to meet each other, and form thus a complete ring, so that the 

 pedicel has at its base the strange appearance of a ring of vascular bundles surrounding 

 a pseudomedullary mass of ground- tissue with both an external and an internal endo- 

 dermis. This structure is retained even after the vascular bundles have taken up 

 the radial arrangement typical for a root stele, which they do long before the root 

 attains a cortex of its own. As the pedicel contracts to form the narrower cylinder of 

 the root itself, the pseudomedullary tissue and the internal endodermis gradually 

 disappear. After the departure of a root the remaining portions of the arc of root- 

 bearing bundles either fuse up again as before, or form separate groups until the next 

 root is to be given off, when the same proceeding is repeated. 



In Cabomba and Nelumbium the rhizomes bear adventitious roots in the same manner 

 at the nodal regions on special steles, which pass directly outwards, but only reach a 

 short distance before they break up into an umbel of roots all springing from about the 

 same point. 



In Cabomba aquatica it appears that only the sympodial rhizome bears roots : the 

 floating shoots bear no roots at all. The comparatively stout stele is very short, and 

 consists of a mass of xylem elements scattered in the central conjunctive tissue, and 

 surrounded by a narrow ring of phloem, in which separate bundles can hardly be 

 distinguished. 



SECOND SERIES. — BOTANY, VOL. V. 2 U 



