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Show 196 DROSERA ROTUNDIFOLIA. CHAP. VIII. an immersion of 8 hrs. 20 m. the loaves wore washed and placed in water; next morning, after about 16 hrs., they wore still inflected and discoloured; on the succeeding day they were evid ently dead. Two leaves were immersed in a stronger mixture, of one part to fifty of water; in 1 hr. 15 In. tho glands became as white as porcelain, as if they had been dipped in boiling water; very few of the tentacles were inflected; but after 4 hrs. almost all wore inflected. These leaves were then placed in water, and next morning wore evidently dead. Half-minim drops of the same strength (viz. one part to fifty of water) were next placed on the discs of five loaves; after 21 hrs. all the outer tentacles wore inflected, and the leaves appeared much jnjurod. I likewise touched the secretion round a large number of glands with minute drops (about •io of a minin1, or ·00296 ml.) of Scheele's mixture (6 per cent.); the glands first became bright red, and after 3 hrs. 15 m. about two-thirds of tho tentacles hearing these glands wore inflected, and remained so for the two succeeding days, when they appeared dead. Conclud~£ng Remarks on the Action of Acids.-It is t•vident that acids have a strong tendency to cause the inflection of the tentacles;* for out of tho twenty-four acids tried, nineteen thus acted, either rapidly and energetically, or slowly and slightly. This fact is renunkable, as the jnices of many plants contain more acid, judging by the taste, than the solutions e1nployed in 1ny experiments. From the powerful effects of so 1nany acids on Drosera, we are led to infer that those naturally contained in the tissues of this plant, as well as of others, must play some important part in their economy. Of the five cases in which acids did not cause tho tentacles to be inflected, one is doubtful; for uric acid did act slightly, and caused a copious secretion of 1nucus. l\1ere sourness to the taste is no * According to l\L Fournier ('De la Fecondn.tion dans los Phanerogamcs,' 1863, p. 61) drops of acetic, hydrocyanic, and sulplmric acid cause the stamens of Berberis instantly to close ; though drops of wa tor h a vc no such power, which latter statement I can confirm. CHAP. VIII. CONCLUDING REMARKS, ACIDS. 1U7 criterion of. the . power of an aCI· a on D roscra, as 1. t rw. ~nd t~rtanc aCids are very sour, yet do not excite Infl:ction. It is remarkable how acids differ in theu power. Thus, hydrochloric acid acts f;.tr l ss powerfully than hy<lriodic and many other acids of the same _strength, and is not poisonous. This is an interestln~ fact, as. hydrochloric acid plays so important a. _pa~t In the digestive process of animals. ] ormic ac1d Induces v_ery slight inflection, and is not poisonous; whereas It~ all!, acetic acid, acts rapidly and powerfully: a~d 1s poisonous. Malic acid acts slightly wher:as ~Itr:c and tartaric acids produce no effect. Lactic acul Is poisonous, and is remarkable from in·· clueing inflection only after a considerable interval of time. Nothing surprised me more than that a solution of benzoic acid~ so weak as to be hardly acidulous to th~ taste, should act wit_h great rapidity and be highly poisonous; for I am Informed that it produces no marked effec~ on the anin1al economy. It 1nay be seen: by look~ng down the list at the head of this disc~ sslon, that :most of the acids are poisonous, often ~Ighly so. ~1luted acids ~re known to induce negatl~ e osmose, and ~he poisonous action of so many acids on Drosera 1s, perhaps, connected with this power,_ for we have seen that the fluids in which they were Immersed oft_en became pink, and the glands pale-coloured or white. Many of the poisonous acids such as h ydrioclic, benzoic, hippuric, and carbolic (bu ~ I_ neglected to record all the cases), caused the secretion of an extraordinary amount of mucus, so that long ropes of this matter hung from the leaves when they were lifted out of the solutions. Other acids, such as hydrochloric and malic, have no such ten- * Miller's 'Elements of Chemistry,' part i. 1867, p. 87. |