Ch apter X —169— Drosera 



The presence of acid being a condition for peptic digestion, he observed 

 that the inner tentacles of the disc of the leaf were more acid than the 

 outer. This may have been because of the greater number of tentacles 

 per unit of area. Darwin thought that the acidity of the secretion of 

 the leaf is increased on the absorption of nitrogenous substances de- 

 rived from the captured insect. 



Opposed to the general trend of opinion was that of Morren 

 (1875), Batalin (1877), TiscHUTKiN (1889), and of Dubois (1899), all 

 of whom were persuaded that the digestion of insects by Drosera is 

 always the result of bacterial action, so that the results of others, to 

 be detailed below, were not without opposition. 



Rees and Will (1875) made a glycerin extract of the leaves and 

 found it weakly acid and to contain an enzyme which in the presence 

 of weak HCl exercised a peptonizing action. Lawson Tate (1875) 

 collected the secretion from the tentacles, sweeping the leaves with a 

 feather (he used Drosera dichotoma), mixed it with water and pre- 

 cipitated it with cholesterin. The precipitate was found to coagulate 

 milk, and this he referred to the action of a ferment which he named 

 droserin. In 191 1 Miss J. White reinvestigated the matter; leaves 

 were removed, washed with previously boiled water with added chloro- 

 form and chopped with a sterile knife. The bits were then placed in 

 lukewarm boiled water with chloroform as antiseptic, shaken vigor- 

 ously for 2 hours. To the filtrate was added an equal part of satu- 

 rated ammonium sulfate, from which a filtrate was obtained which 

 contained a principle which could attack fibrin but only in an acid 

 medium. The product gave the biuret reactions. Abderhalden 

 (1906) had found that in its presence peptides are not spHt. 



Dernby in 191 7 obtained a glycerin extract of the leaves from 

 which by means of dialysis he obtained an enzyme which he regarded 

 as a pepsin. This worked at an acidity of pR 5 as optimum. No 

 tryptase or ereptase was found. 



Miss Robinson (1909) tested the digestive effect of Drosera on 

 " purer proteins" then available. She found that acid-albumin, alkali 

 albuminate and edestin were digested, but " somewhat less readily" 

 than dry egg-white, fibrin, tendo-mucoid and nucleoproteins. Col- 

 lagen and elastin proved entirely indigestible. Though creatin did not 

 cause a bending of the tentacles, it was readily dissolved, meanwhile 

 remaining in contact with the leaf for three days. It is important, in 

 view of Darwin's opposed idea, that the lack of movement of the 

 tentacles is not an indication of the non-nutritional value of the sub- 

 stances applied; nor did Darwin find that the positive response indi- 

 cates the contrary. 



Beginning in 1930 Okahara pubHshed a series of papers deahng 

 with the matter. He first dealt with the question of the actual oc- 

 currence of a digestive ferment in Drosera. The leaves were extracted 

 with glycerine and water for several days (with toluene) and the press 

 juice then filtered off. The mother solution thus obtained showed 

 strong acidity. The enzyme was separated by means of acetone and 

 redissolved for experimentation. 



He concluded that there exists in the leaves of Drosera a powerful 

 proteolytic enzyme which, acting on proteins, hydrolyses them to 



