DARWIN'S INSECTIVOROUS PLANTS. 209 



Mr. Darwin next records various observations and experi- 

 ments upon more ordinary glandular hairs of several plants. 

 To certain Saxifrages his attention was naturally called, on 

 account of the presumed relationship of Droseracece to this 

 genus. He declares that " their glands absorb matter from 

 an infusion of raw meat, from solutions of nitrate and carbon- 

 ate of ammonia, and apparently from decayed insects." To 

 such plants the vast number of little insects caught may not 

 be useless, as they may be to many other plants (Tobacco, 

 for instance) with sticky glands, in which Mr. Darwin could 

 detect no power of absorption. The prevalent idea, that 

 glandular hairs in general serve merely as secreting or excret- 

 ing organs, and are of small or no account to the plant, must 

 now be reconsidered. Those of the common Chinese Primrose 

 {Primula Sinensis), although indifferent to animal infusions, 

 were found to absorb quickly both the solution and vapor of 

 carbonate of ammonia. Now, as rain-water contains a small 

 percentage of ammonia, and the atmosphere a minute quan- 

 tity of the carbonate or nitrate, and as a moderate-sized plant 

 of this Primrose was ascertained (by estimate from a count 

 on small measured surfaces by Mr. Francis Darwin) to bear 

 between 2| to 3 millions of these glands, it begins to dawn 

 upon us that these multitudinous organs are neither mere 

 excrescences nor outlets, nor in any just sense insignificant. 



Mr. Darwin next investigates the densely crowded short 

 glandular hairs, with their secretions, which form the buttery 

 surface of the face of the leaves of Pinguicula, the Butter- 

 wort. He finds that the leaves of the common Butterwort 

 have great numbers of small insects adhering to them, as also 

 grains of pollen, small seeds, etc. ; that most substances so 

 lodged or placed, if yielding soluble matter -to the glands, 

 excite them to increased secretion ; but that if non-nitrogenous 

 the viscid fluid poured out is not at all acid, while if nitro- 

 genous it invariably has an acid reaction and is more copious ; 

 that in this state it will quickly dissolve the muscles of insects, 

 meat, cartilage, fibrin, curds of milk, etc. ; that when the 

 surface of a plane leaf is fed, by placing upon it a row of 

 flies along one margin, this margin, but not the other, folds 



