16 



when Mr. Ellis sent a short account of one of these plants 

 to the Swedish Natural History Society. In 1857 Livingstone 

 mentioned that he had observed a plant in South Africa which 

 frequently caught insects. It was a Drosera. But it was not 

 until 1875, when Darwin published his book on " Insectivorous 

 Plants," that any great interest was taken in the subject. 



Plants feed partly upon mineral substances, which they 

 draw up by their roots, and partly upon air, which they take in 

 by their leaves. The wood of plants, or "cellulose," which is 

 approximately composed of seven parts by weight of carbon, 

 one of hydrogen, and eight of oxygen, is almost entirely taken 

 up from the air. Plants also have some nitrogen in their 

 composition. This is required for the production of protoplasm 

 the active part of the plant, and is, as a rule, obtained from 

 the soil. Now if plants could obtain their nitrogen directly 

 from animals, in the tissues of which compounds containing 

 nitrogen preponderate, they would not require large roots, and 

 they might therefore flourish where large-rooted plants could 

 not grow. Insectivorous plants have smaU roots. One of the 

 results of Mr. Darwin's investigations was the discovery that 

 many of the insect-eating plants belonged to the same natural 

 family, and it is particularly interesting to notice, for instance, 

 that several of the best-known examples of this class belong to 

 a family so well characterised on purely structural grounds as 

 that of the " bladderworts," or the Lentibulariacese. 



In the Pingwicula the leaves are found slightly turned in, 

 and studded with a number of glands, some of which are stalked 

 and some unstalked. These glands constantly exude a viscid 

 secretion, which besmears the whole surface of the leaf. The 

 object of this sticky secretion is to catch insects. Insects alight 

 on the leaves and cannot get away, owing to the adhesiveness 

 of the secretion. The edge of the leaf then turns in, and grasps 

 the victim so that it is perfectly entrapped. The insect finally 

 becomes quite enveloped, a large number of glands is brought 

 into contact with it, and the creature becomes slowly digested. 

 The plant, however, only selects food which contains nitrogen. 

 It can digest very refractory substances, so long as they contain 



