Hippuric Acid.—­Four leaves were immersed in 120 minims of a solution of 1 gr. to 437 of water.  After 2 hrs. the fluid was coloured pink; glands pale, but no inflection.  After 6 hrs. some inflection; after 9 hrs. all four leaves greatly inflected; much mucus secreted; all the glands very pale.  The leaves were then left in water for two days; they remained closely inflected, with their glands colourless, and I do not doubt were killed.

Hydrocyanic Acid.—­Four leaves were immersed, each in thirty minims of one part to 437 of water; in 2 hrs. 45 m. all the tentacles were considerably inflected, with many of the glands pale; after 3 hrs. 45 m. all strongly inflected, and the surrounding fluid coloured pink; after 6 hrs. all closely inflected.  After [page 196] an immersion of 8 hrs. 20 m. the leaves were washed and placed in water; next morning, after about 16 hrs., they were still inflected and discoloured; on the succeeding day they were evidently dead.  Two leaves were immersed in a stronger mixture, of one part to fifty of water; in 1 hr. 15 m. the 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 were inflected.  These leaves were then placed in water, and next morning were evidently dead.  Half-minim drops of the same strength (viz. one part to fifty of water) were next placed on the discs of five leaves; after 21 hrs. all the outer tentacles were inflected, and the leaves appeared much injured.  I likewise touched the secretion round a large number of glands with minute drops (about 1/20 of a minim, 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 the tentacles bearing these glands were inflected, and remained so for the two succeeding days, when they appeared dead.]

Concluding Remarks on the Action of Acids.—­It is evident that acids have a strong tendency to cause the inflection of the tentacles;* for out of the twenty-four acids tried, nineteen thus acted, either rapidly and energetically, or slowly and slightly.  This fact is remarkable, as the juices of many plants contain more acid, judging by the taste, than the solutions employed in my experiments.  From the powerful effects of so many 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 the tentacles to be inflected, one is doubtful; for uric acid did act slightly, and caused a copious secretion of mucus.  Mere sourness to the taste is no

* According to M. Fournier (’De la Fcondation dans les Phanrogames.’ 1863, p. 61) drops of acetic, hydrocyanic, and sulphuric acid cause the stamens of Berberis instantly to close; though drops of water have no such power, which latter statement I can confirm; [page 197]