296 ME. D. T. GWYNNE-VAUGHAN ON THE 



The Occurrence of Folystehj. 



During the progress of these investigations my attention was directed by the Curator 

 of the Gardens, Mr. Watson, to certain remarkably elongated stolons or runners borne 

 laterally on the rhizomes of Ny7nphcea flava. They are found below the surface of the 

 soil, and are evidently produced in order to ensure the survival of the plant through 

 those seasons of the year which are unfavourable to its continued growth, and at the 

 same time to increase the number of individuals. Similar functions are performed by 

 the laterally produced tubers in Kymph(Ba tuherosa. 



The stolons of J^, flava attain a considerable length (30-40 cm.), and are slightly 

 thickened at their terminations, where they bear a number of short tuberous starch-Jaden 

 roots on their under surface, and on their upper surface a number of buds protected 

 by scale-leaves (PI. XXII. fig. 15). In these stolons the vascular bundles are arranged 

 in 4-5 widely separated groups lying in a uniformly lacunar ground-tissue, with a 

 rather abruptly marked off hypodermal zone of continuous parenchyma (fig. 16). Each 

 group consists of 3-4 vascular bundles arranged around a central canal which has taken 

 the place of their disintegrated protoxylems, the remains of which are still to be seen at 

 the borders of the lacuna. The phloem groups, on the other hand, are well developed 

 and very prominent; seen in transverse section they are ovate in outline and quite 

 distinct from each other. In greater part they are composed of sieve-tubes of excep- 

 tionally large lumen accompanied by their companion cells, while on the outside there is 

 a small cap of phloem parenchyma. Only a few of the later formed elements of the 

 xylem are persistent on the inner side of the phloem groups ; they are separated by 

 several parenchymatous cells from the central canal. At either end of the runner this 

 xylem is considerably increased in amount, and its elements fill up the space elsewhere 

 occupied by the canal. A beautifully-marked endodermis surrounds each group 

 completely ; so that each of them exhibits in itself all the essentials of a complete stele 

 (fig. 17). It is curious to note that in the cells of the endodermis the fold on the radial 

 walls is rarely placed exactly in the centre, but is nearly always situated nearer to the 

 inner tangential wall than to the outer — an idiosyncrasy which is also a characteristic 

 of the polystelic Primulas and Gunneras. Approaching the termination of the runner 

 where the buds and tuberous roots are borne, the ground-tissue becomes continuous 

 throughout, the lacunae disappearing; the bundles in each stele become confused and 

 indistinct ; and at certain intervals, in relation to the insertion of the buds, the steles 

 themselves fuse up into an irregular circle, beyond which they scarcely regain their 

 identity before they enter into another similar fusion, and so on. 



In A^. Uiherosa the stalks which bear the tubers are very short, not more than 4 cm. 

 long, some of the tubers being almost sessile. Their structure in all cases examined is 

 essentially similar to that of the runners of N. flava, 3-5 separate steles being present, 

 each composed of 3-5 vascular bundles, although here the ground-tissue is without 

 lacunae, aud the bundles within each stele are less distinctly separated from one another. 

 The \vhole structure is, in fact, closely comparable to that of the runners of N. Jlaca 

 near their tuberous bud-bearing extremities. 



