28o THE BIOLOGY OF FLOWERING PLANTS 



by leaves in the genus. In U. Jamesoniana, a species 

 creeping on the trunks of trees in Ecuador, there are elliptical 

 foliage leaves and linear foliage leaves, the latter alone bear- 

 ing on the margins stalked bladders (Fig. 40). In U. affinis, 

 no foliage leaves are produced from the base of the inflores- 

 cence, but only " rhizoid " leaves and homologous *' run- 

 ners." The latter bear bladders and spatulate foliage 

 leaves. These runners are probably not shoots but again 

 modified leaves. In other species the leaves, borne by such 

 runners, may give rise to runners, or to other leaves. It is 

 thus probable that, what in our native species appear to be 

 axes bearing leaves, are leaves only. These complicated re- 

 lationships are discussed by Arber and by Goebel. Utri- 

 cularia is in fact a plant in which the ordinary mode of 

 organisation of the dicotyledons is largely abandoned ; the 

 distinctions between leaf and axis can no longer be logically 

 carried through. A different interpretation of the mor- 

 phology is given by Compton (1909). 



Biovularia is a monotypic West Indian genus, in habit 

 like a small water Utricularia : Polypompholjoc, with three 

 tropical species, resembles small land Utricularias. Genlisea, 

 however, a genus with ten species, mostly Brazilian, has a 

 remarkable and unique habit. It is a land plant with a 

 dense rosette of small spatulate leaves, from which arise 

 the inflorescences. It has no roots, but is anchored in the 

 soil by long white rhizoids, each with a forked tip. Each of 

 the two branches of the fork is twisted into a close cork- 

 screw (Fig. 41) . The rhizoid, which is homologous with the 

 leaf, has a slender basal stalk a few centimetres long : it then 

 swells out into a small bladder, about i mm. in internal 

 diameter, the hollow of which is prolonged into a narrow 

 canal, not more than ^ mm. in diameter, which runs through 

 the distal portion of the rhizoid and opens in a narrow slit 

 below the forked end. In the young rhizoid the branches 

 of the fork lie closely together so that penetration of the soil 

 is possible ; later they spread out. The whole arrangement 

 is an extraordinary transformation of the Utricularia bladder, 

 suited to the capture of minute soil organisms, with the 



