160 DROSERA ROTUNDIFOLIA. (Cuap. VIII. 
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 an immersion of 8 hrs. 20 m. 
the leaves were washed and placed in water; next morning, alter 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 filty 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 sj, of a minim, 
or *00296 c.c.) of Scheele’s mixture (containing 4 per cent. of anhydrous 
acid); 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 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 criterion of the power of an acid on Drosera, 
as citric and tartaric acids are very sour, yet do not excite 
inflection. It is remarkable how acids differ in their power. 
Thus, hydrochloric acid acts far less powerfully than hydriodic 
* According to M. Fournier (‘De cause the stamens of Berberis in- 
la Fécondation dans les Phanéro-  stantly to close; though drops of 
games,’ 1863, p. 61) drops of acetic, water have no such power, which 
hydrocyanic, and sulphuric acid latter statement I can confirm. 
