. British plants; their biology and ecology. Botany; Botany; Plant ecology. 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
. British plants; their biology and ecology. Botany; Botany; Plant ecology. 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.—Pinguicv
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