OCR Text |
Show 96 DROSERA ROTUNDIFOLIA. CHAP. VI. process of dI.g es t1' 0n now commenced ' so that within 48 hrs. from1 the time when the acid was given the fou~ cufibeds we 1 .bre not on y comp l et el y dI.S S olved , but much of the hque e a umen was absorbed·. t 11-Two cubes of a lbu men ( 1 f 'ncb · 40 o an I , or Expenm)en, ·placed on two leaves and were treated with ·635 mm. were ' . al lr a lI.e s as I· n the la·s t experiment ' and with the hs ame 1re su·l t; for after 22 hrs. they had their angles perfectly s arp, s 10wmg that the digestive process had been completely arres.ted. I then wished to ascertain what would L~ the effect of using stronger hydrochloric acid; so I added minute drops of the strength of 1 t This proved rather too strong, for after 48 hn;. per cen . d b t'll from the time when the acid was adde . one cu e was s I almost perfect, and the other only yery slightly rounded, and both were stained slightly pink. This latter fact shows ~bat ~he leaves were injured,* for during the normal process of digestiOn the albumen is not thus coloured, and we can thus understand why the cubes were not dissolved. From these experiments we clearly see that the secretion has the power of dissolving albumen, and. we further see that if an alkali is added, the process of digestion is stopped, but im~ediately recommences ~s soon as the alkali is neutralised by weak hydrochlonc acid. Even if I had tried no other experin1ents than these, they would have almost sufficed to prove that the glands of Drosera secrete some fermen~ an~logous to pepsin, which in presence o~ an acid ?Ives to the secretion its power of dissolving albuminous compounds. Splinters of clean glass were scattered on a lai:ge number of leaves, and these became moderately Inflected. They were cut off and divided into. thr~e lots ; two of them, after being left for some time In a little distilled water, were strained, and some dis- * Sachs remarks (' Traite de Bot.' 1874, p. 774), that cells which are killed by freezing, by too great heat, or by chemical ao-ents allow all their colouring 0 matter' to escape m• to the sur-rounding water. s CHAP. VI. DIGESTION. 97 coloured, viscid, slightly acid fluid was thus obtained. The t~ird lo~ wa.s well soaked in a few drops of glycenne, which Is well known to dissolve pepsin. Cubes of album en ( cio of an inch) were now placed in the three fluids in watch-glasses, some of which . were kept for several days at about 90° Fahr. ( 32°·2 Cent.), and others at the temperature of my room; but none of the cubes were dissolved, the angles. re:naining as sharp as ever. This fact probably Indicates that the ferment is not secreted until the glands are excited by the absorption of a minute quantity of already soluble animal matter,-a conclusion which is supported by what we shall hereafter see with respect to Dionrea. Dr. Hooker likewise found that, although the fluid within the pitchers of N epenthes possesses extraordinary power of digestion, yet when removed from the pitchers before they have been excited and placed in a vessel, it has no such power, although it is already acid; and we can account for this fact only on the supposition that the proper ferment is not secreted until some exciting matter is absorbed. On three other occasions eight leaves were strongly excited with albumen moistened with saliva; they were then cut off, and allowed to soak for several hours or for a whole day in a few drops of glycerine. Some of this extract was added to a little hydrochloric acid of various strengths (generally one to 400 of water), and minute cubes of albumen were placed in the mixture.* In two of these trials the cubes were not in the least acted on· but in the thjro ' * As a control experiment bits of albumen were placed in the sa~e glycerine with hydrochloric aCid of the same strength ; and the albumen, as might have beeu expected, was not in the least affected after two days. H |