44o The Physiology of Plants book hi 



Burdon Sanderson showed in 1873, and more fully in 

 1882, that electrical phenomena, comparable with those 

 attending muscular contraction, are manifested during the 

 closing of the leaf. 



Aldrovanda, a near relative of Dionaea, and possessing 

 a similar mechanism, was investigated by Cohn in 1875, 

 and by Darwin in the same year. Darwin found that 

 Saxifraga umbrosa possesses the power of absorbing an 

 infusion of raw meat. He proved also that all these hetero- 

 trophic plants can absorb dilute solutions of ammonia and 

 of ammonium carbonate, and was inclined to regard this 

 power as bearing on such absorption from the air, and from 

 rain-water, in which traces of these compounds are present. 



Another plant which was in the first instance investi- 

 gated by Darwin was Pinguicula vulgaris ; he found it 

 capable of digesting not only the bodies of insects, but 

 such vegetable structures as pollen grains, leaves, and seeds 

 of other plants which may fall upon its leaves. Two other 

 species of the genus gave similar results. 



Utricularia, a plant which in some respects resembles 

 the pitcher plants, to which allusion has been made, was 

 the subject of observation by Crouan in 1858, and by 

 Holland ten years later. Both writers found small aquatic 

 insects imprisoned in its bladders. An important memoir 

 on this plant was published by Cohn in 1875, and it figured 

 prominently in Darwin's researches published in the same 

 year. Its operations were carefully watched and explained 

 by Mrs. Treat at about the same time. Further observa- 

 tions upon it were made by Schimper in 1882. Neither 

 observer was able to detect with certainty a true digestive 

 process in the bladders, though Darwin held that the 

 appearances justify a suspicion that an enzyme exists. In 

 the absence of such an agent the cause of the disintegra- 

 tion of the captives must be ordinary putrefaction. All 

 these writers agreed that the products of decay or digestion 



