ECOLOGICAL 165 



for it has been observed that death follows quickly in young and 

 abundantly secreting bladders, which are coloured reddish with 

 anthocyan in the common species, while the prisoners may swim 

 about for days in those that are older, and have their anthocyan 

 changed into blue. Over the internal surface of the bladder there are 

 minute quadrifid hairs, and it has been experimentally proved that 

 these absorb organic substances. After the bladders have been fed 

 with a Httle of the fatty substance called lecithin, globules are seen 

 in the quadrifid hairs. There is also a secretion of a digestive ferment, 

 and along with that a little benzoic acid, which probably prevents 

 premature putrefaction of the victims. The pecuUar four-armed 

 hairs are connected by intergrades to the much larger external hairs; 

 and it should be noticed that similar hairs occur on various aquatic 

 plants, e.g. Callitriche verna, which have no carnivorous habits. 

 Finally, the evidence is completed by Biisgen's observation that 

 bladderworts from which all water-fleas were carefully excluded did 

 not thrive so well as those in quite normal conditions. As a possible 

 instance of a play within a play, we may mention, though with some 

 doubt, the observation that the water-spider (Arg5^oneta) sometimes 

 rifles the little bladders of Utricularia. 



In the summer months the straggUng stem of the common bladder- 

 wort, with its much divided slender leaves and its hundreds of 

 "bladders", floats at the surface, and grows at one end as it dies 

 away at the other. Towards the end of summer the life of the plant 

 becomes concentrated in the thick-set terminal tuft, which is 

 weighted with reserve products. As in some other aquatic plants, 

 this terminal tuft breaks off and sinks to the bottom, remaining in 

 a resting state through the winter. In spring it begins again to grow, 

 and somewhat lightened rises to the surface to recommence the 

 cycle. This fact led A. P. de Candolle and some other botanists to 

 the mistaken view that the bladders functioned as floats. In 1852 

 de Candolle said that the young bladders were filled with mucus, 

 which, being heavier than water, kept them at the bottom, but the 

 mucus was gradually replaced by gas, which buoyed the plant to 

 the surface. There is no doubt as to the sinking of the terminal 

 tuft and its floating up again, but the bladders are not concerned. 

 As Darwin showed, a bladderwort floats as usual after its bladder 

 are all cut off — which must have taxed even Darwin's patience. 

 Moreover, there are many non-aquatic Utricularias v/hich have 

 nevertheless thousands of bladders. There is no doubt whatever that 

 the bladders serve as traps, even in the terrestrial species. They are 

 known to capture minute terrestrial animals which creep about in 

 damp places or on the mossy stems of trees. 



It is ecologically interesting to notice special adaptations to the 

 diverse habitats of bladderworts. The aquatic forms have some- 

 times air reservoirs which act as buoys for the upright flower-stalk ; 



