848 



THE DISPERSION OF SPECIES BY MEANS OF FRUITS AND SEEDS. 



these circumstances that can supply the propelling force necessary to drive such 

 fruits and seeds as can keep afloat from one shore to another. Special mention 

 must be made of three groups of fruits and seeds belonging to this category. These 

 are, firstly, dry fruits which are rendered buoyant by air-inclosing envelopes, as, for 

 instance, in the case of the marsh-plants known as Sedges (Car ex ampullae- a, 

 C. vesicaria, &a), where the fruit is surrounded by an inflated utricle; secondly, the 

 fruits of Water- Plantains, Flowering-rushes, &c. (Alisma, Butomus, Sag itt aria, 

 Sparganium, &c.), which are furnished with a thick air-filled cortical parenchyma; 

 and, thirdly, the seeds of some Water-lilies. In the case of the white Water-lilies 



461 Dispersion of fruits and seeds by the wind. 



(NympJum), each seed is enveloped in a coat (amttus), which loosely clothes the 

 outer integument (testa) of the seed, so as to leave a layer of air between the two. 

 the species of the genus Nuphar there is no arillus, but the carpels separate 

 the fruit is ripe into two layers, of which the outer one is green and succulent 

 inner one is white and charged with air, and incloses a large number of 

 In all these cases the seeds are enabled to float by their envelopes, and are 

 riven along on the surface of the water by the wind. 



n a similar manner the wind causes certain detached as well as aggregated fruits 

 torol along upon level ground. This phenomenon is observed particufarly in regions 



Id lo ST , ? Ught f UOWS ^ Sh rt SUmmer Season of development; 



Uedite t V P , 1WltS Q COI1Cemed are "Penally abundant in the vicinity of the 



ranean Sea and in Steppe-lands. Several Umbellifers indigenous to the Wh. 



