INSECTIVOROUS PLANTS 



131 



with multitudes of flying insects, they become veritable 

 cemeteries. 



Both of these plants live in bogs, the butterwort, on 

 the whole, preferring the sweeter parts, while the sundew 

 is indifferent. In bogs the water is sour and deficient in 

 nitrates. There is plenty of nitrogen present, but, as it is 

 mostly in the form of humous acids or ammonium-com- 

 pounds, little use can be made of it. The insectivorous 

 habit in these bog-plants is correlated with the need for 

 nitrogen in a place where it is deficient. Not being able 

 to get sufficient from the soil, the plants entrap living 

 insects, and secure a supply of 

 protein from the dissolving bodies 

 of their prey. 



(c) Utricularia vulgaris, bladder- 

 wort (Fig. 46), a submerged free- 

 floating aquatic found in ditches. 

 It has no roots. The leaves are 

 large and much-divided, floating in 

 suspension just below the surface 

 of the water. In summer the 

 flowering shoots emerge from the 

 water, lifting into the air a spike 

 of conspicuous flowers, pollinated 

 by insects. Upon the submerged 

 leaves, at the base of some of the 

 green, thread-like segments, occur 

 small, bladder - like structures, 

 which give the plant its name 

 (Lat. utriculum, a bladder). Each 

 of these hollow chambers is pro- 

 vided with a hinged door, which is easily opened 

 from without, but cannot be opened by pushing from 

 within. Over the entrance is a brush of bristling hairs, 

 and round the mouth of the bladder occur a number 

 of glandular hairs. Small Crustacea, such as Cyclops 

 (water - fleas), poking about among these hairs for 

 food, and possibly attracted by the secretions of the 

 glandular hairs, push open the trap-door and enter the 

 chamber. The door closes behind them, and they are 

 entrapped. Inside, they soon die either of suffocation or 

 starvation, and the products of their decaying bodies are 

 absorbed. The interior walls of the bladder are covered 



Fio. 45. — Pinguicvla vul- 

 garis (Butterwort). 



