VIIl] 



ANATOMY OF BLADDERWORTS 



107 



Fig. 73. Utricularia vul- 

 garis, L. Developing leaf 

 showing two young blad- 

 ders 61 and h.^; m.g., muci- 

 lage gland. (Enlarged.) 

 [Meierhofer, H. (1902).] 



of the available evidence regarding the nature of the organs in 

 the Bladderworts, seems to be that in the present state of our 

 ignorance the attempt to fit so elusive 

 a genus .into the Procrustean bed of 

 rigid morphology, is doomed to failure. 

 It is probably best, as a purely provisional 

 hypothesis, to accept the view that the 

 vegetative body of the Utricularias par- 

 takes of both stem nature and leaf nature. 

 How such a condition can have arisen, 

 historically, from an ancestor possessing 

 well-defined stem and leaf organs, remains 

 one of the unsolved mysteries of phylo- 

 geny. 



The anatomy^ of the water Utricu- 

 larias, though showing some curious 

 features, is less anomalous than their 

 morphology. In the stem of U. vulgaris, 

 the tracheids, of which one or more are present, are placed 

 sub-centrally, and surrounded by little groups of phloem. 

 Some degree of dorsiventrality is given to the structure by 

 the thin-walled character of the small lower sector of the 

 vascular cylinder in which the tracheids lie, while the con- 

 junctive tissue of the rest of the stele, towards the upper 

 side of the axis, is fibrous. The tracheal elements are of 

 the nature of "imperfect vessels," being formed from a file of 

 superposed cells, with imperforate, oblique, separation walls. 

 The incompleteness of the conducting elements is probably to 

 be associated with the relative unimportance of the transpira- 

 tion stream in a rootless submerged plant. The vascular cylinder 

 is surrounded by an endodermis, and the cortex is lacunar. The 

 structure of the inflorescence-axis differs very markedly from 

 that of the submerged stem; the tracheids form a discontinuous 

 ring enclosing a large central pith containing phloem islands. 



1 Tieghem, P. van (1868) and (1869I}, Russow,E. (1875), Schenck,H. 

 (1886) and Hovelacque, M. (i888). 



