1902 Marsh Botany in spring 131 



of this Magazine, rise to the surface of the water in summer, 

 sinking to the bottom at the approach of winter. When 

 they rise to the surface they are buoyed up by a number 

 of little bladders or vesicles interspersed, in most species, 

 among the hair-like segments of the submerged leaves. 

 These bladders are the plant's insect-traps, for each has 

 an orifice fringed with stiff bristles and furnished with a 

 valve-like door or shutter which opens to the slightest 

 pressure from without. "Abandon hope all ye who enter 

 here " might well be inscribed over these dread portals, 

 for no aquatic insect that enters ever emerges, but is, 

 like those which settle on the viscid leaves of the sun- 

 dews, absorbed by certain specially constructed cells, with 

 which, in the case of the bladderworts, the interior of 

 each bladder is lined. These cells, writes Professor von 

 Marilaun, are '* linear-oblong, and somewhat like little 

 rods in shape, and they line the whole internal surface of 

 the cavity of the bladder. They are arranged in fours, 

 each group of four forming a cross, and being united by 

 a common basal cell. The basal cells themselves are 

 intercalated amongst the cells lining the bladder. The 

 organic substances from the decaying bodies of captured 

 animals are sucked up by these stellate groups of cells, 

 and from them pass into the basal cells, and later into 

 the other adjacent cells of the bladder and those of the 

 plant at large." Rotifera and infusoria constitute the prin- 

 cipal food of these carnivorous plants ; but the larvae of 

 gnats are also captured and consumed. U . minor seems 

 to be the most insatiable of our native species, and some 

 remarkable lists of the contents of its bladders have been 

 compiled. The bladderworts are distributed over nearly 

 the whole world. Most of them are water plants, — one 

 exists solely in the rain-filled receptacles of Tillandsia 

 plants, — but a few grow among mosses and lycopods, in 

 rock crevices, and the bark-fissures of old trees. Of the 

 three British species — U. vulgaris, minor, and intermedia — 

 U. minor is the commonest, and U. vulgaris has the widest 

 distribution. 



I have left myself no space in which to deal with the sedges, 

 nearly all of which flower in spring and early summer. 



