[ 91 J 



CHAPTER VIII 



THE LIFE-HISTORY OF THE AQUATIC 

 UTRICULARIAS AND OF ALDROVJNDIA 



OF all our native aquatics, the Bladderworts (Utricularid) 

 diverge most in their vegetative characters from ordi- 

 nary terrestrial plants. When not in flower, they live wholly 

 submerged. Roots are entirely absent and the plant consists of 

 an elongated branching axis producing delicate, finely-divided 

 leaves on which small utricles are borne. This is not, however, 

 the only type of vegetative body represented in the genus. 

 Outside Europe there are a number of terrestrial species in 

 which entire leaves of a simple type are produced in addition 

 to bladder-bearing organs. The family to which the genus be- 

 longs Lentibulariaceae consists chiefly of aquatic and marsh 

 plants; it is probable that the water Utricularias, with which 

 alone we are concerned in this chapter, are the descendants 

 of marsh forms, which, in the course of evolution, have become 

 more and more completely involved in aquatic life^. It is im- 

 possible to draw a sharp line within the genus between the land 

 and water types; the terrestrial species sometimes produce 

 water forms, and the aquatic species can, to a limited extent, 

 take to life on land. Even among our native Bladderworts, we 

 find that, though Utricularia vulgaris cannot live except as a 

 submerged plant, U. minor and TJ. intermedia are able, on rare 

 occasions, to produce land forms^, which are so far adapted to 

 aerial life as to develop stomates but in this condition they 

 do not flower. The land form of V, minor is said to grow as a 

 close moss-like turf. 



The little utricles borne by the leaves (Fig. 59, p. 92), which 

 give the Bladderworts their unique appearance, and to which 



iGoebel, K. (1891-1893). 



2 Gliick, H. (1906) and Luetzelburg, P. von (19 10). 



