1883-84.] Edinburgh Naturalists' Field Club. 161 



Insects are induced to visit the honey secretion of the lid and 

 mouth of the pitcher, and are thus led on to the conducting surface. 

 This affords no foothold, and they glide down till they reach the 

 detentive surface. When once amongst the hairs of this part of the 

 pitcher, there is no possibility of returning, their struggles only 

 serving to wedge them deeper and more firmly. The secretion 

 " wets " an insect much more rapidly than water : but it apparently 

 has no digestive i)roperties, appearing rather to hasten decomposition. 

 The broad wing of the pitcher is also said to be baited with honey, 

 so as to lure insects to their destruction by jsresenting a pathway 

 from the ground. 



Utricularia. 



The British species of this genus are all aquatic, but some exotic 

 species are terrestrial. The aquatic plants are entirely destitute of 

 roots, and the submerged stem and branches are clothed with leaves, 

 which are dissected up into slender filiform segments ; and on these 

 segments numerous little bladders or ampullse are developed. The 

 leaves are tipped with short straight bristles. The plants float near 

 the surface of the water, above which they send their flowers sup- 

 ported on slender stalks. 



In U. vulgaris the bladders are supported on short footstalks, and 



are about xV of ^^ i^^ch in length. They are generally filled with 



j water, but sometimes they contain air-lnibbles. At the apex is a 



small orifice, around which are a number of hair-like prolongations 



[ called antennag. On the inside of this orifice is a small hemispherical 



ralve, which shuts against the rim or collar of the orifice. The 



ralve is elastic, and can be pushed back by a small insect, which 



fthus easily finds admission to the inside of the bladder. When once 



in, there is no chance of its getting out, for the valve springs back 



against the collar and completely closes the entrance. All over the 



[ interior of the bladder small processes called " quadrifids " are placed. 



I These consist of very short stalks, which spring from angular cells at 



j the junctions of the angles of the larger cells ; and at their apices four 



arm-like processes are developed, each of which consists of a single 



I cell. In U. vulgaris two of these arms are long and two short, but 



in U. montana they are aU nearly of the same length. The bladders 



; were supposed by some to act as floats ; but as they seldom contain 



air, it is probable that the plants are floated up by the air contained 



[in the intercellular spaces. The real use of the bladder is to capture 



I small insects, which they do in great numbers. As already men- 



Ktioned, they enter the bladder by pushing back the valve ; and the 



[free edge of this is so thin, and shuts so closely against the collar, 



tthat a Daphnia which Darwin mentions as having inserted one of its 



antenna into the slit was held fast for a whole day. The insects 



[captured are all small water-insects, such as Cyclops, &c. ; and, as in 



