Vesicles uf the Utricularirc. 395 



0*295 gramme; consequently there is a \cxy considerable excess 

 of forccj capable of maintaining the flowers out of the water 

 through the whole time of fecundation. After this act, the 

 utricles gradually become filled with liquid, the specific gravity 

 of the plant increases, and it descends again slowly with its 

 ripening fruits below the level of the water. The seeds, escaping 

 from their unilocular capsule, fall into the mud, where they 

 germinate*. 



We find among authors a difference of opinion as to the po- 

 sition of the Utncularice in the water before flowering. Some 

 regard them as attached to the bottom by slight roots ; others 

 (as, for example, Reinsch) regard them as fioating plants. The 

 Utricularm are really at first attached to the bottom ; but 

 the aeriferous vesicles which are developed upon their leaves 

 gently draw them out of the mud in which their filamentous 

 roots bury themselves ; and it is in this that I find the true 

 utility of the utricles — namely, that they pull up the plant 

 from the bottom ; for the plant alone, without utricles, tloats 

 very well in the water, and rises towards the surfacef. 



The Utricularice, however, are not the only plants in which 

 we see such movements produced by an evolution of gas. In 

 the Hottonice, Aldrovandce, and Trapa natnns we may discern, at 

 the epoch of flovvcring, slow movements of displacement of the 

 entire plant ; whilst in other aquatic plants {Ni/mjj/icra, Vallis- 

 neria, Ranunculus aquaiilis, &c.) only certain parts become elon- 

 gated. In the Utricularice and Aldrovandce it is by aeriferous 

 vesicles that the specific gravity of the plant is diminished and 

 it is caused to rise by being drawn out of the soil. In the 

 Hottonice we find, in the leaflets, cells filled with air. In the 

 petioles of Trapa nutans aeriferous cavities are formed before 

 the flowering (lleinseh, loc. cit.). 



Sometimes the plant cannot perfectly detach itself from the 

 bottom ; the pollen-grains are then preserved in another man- 

 ner from contact with the water. The following is a striking 

 example, which shows us, as in the preceding cases, that at the 

 approach of the flowering-season there is an evolution of gas, 

 which, instead of producuig a movement, plays a more direct 

 j)art in fecundation. 



* The seeds are usually sterile ; but there are large reproductive buds 

 which descend to the bottom of the water during the winter (A. dc Candolie, 

 Geographic Botanique, tome li. p. 1003). 



t I placed in a large glass vessel a tuft of Utricularla furnished with 

 vesicles which were still green ; the ])lants floated at the surface of the 

 water. Some Lymnccce contained in the same vessel gnawed the plants, 

 and es])eeially devoured the utricles ; the Utricidarice, thus deprived of 

 their vesicles, still maintained themselves at the surface. 



