Insectivorous plants / by Charles Darwin ; revised by Francis Darwin.

  • Charles Darwin
Date:
1908
Catalogue details

Licence: In copyright

Credit: Insectivorous plants / by Charles Darwin ; revised by Francis Darwin. Source: Wellcome Collection.

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    glands of the disc are excited by the contact of any object, especially of one containing nitrogenous matter, the outer tentacles and often the blade become inflected; the leaf being thus converted into a temporary cup or stomach. At the same time the discal glands secrete * more copiously, and the secretion becomes acid. Moreover, they transmit some influence to the glands of the exterior tentacles, causing them to pour forth a more copious secretion, which also becomes acid or more acid than it was before. As this result is an important one, 1 will give the evidence. The secretion of many glands on thirty leaves, which had not been in any way excited, was tested with litmus paper ; and the secretion of twenty-two of these leaves did not in the least affect the colour, whereas that of eight caused an exceedingly feeble and sometimes doubtful tinge of red. Two other old leaves, however, which appeared to have been inflected several times, acted much more decidedly on the paper. Particles of clean glass were then placed on five of the leaves, cubes of albumen on six, and bits of raw meat on three, on none of which was the secretion at this time in the least acid. After an interval of 24 hrs., when almost all the tentacles on these fourteen leaves had become more or less inflected, I again tested the secretion, selecting glands which had not as yet reached the centre or touched any object, and it was now plainly acid. The degree of acidity of the secretion varied somewhat on the glands of the same leaf. On some leaves, a few tentacles did not, from some unknown cause, become inflected as often happens; and in five in- stances their secretion was found not to be in the least acid; whilst the secretion of the adjoining and inflected tentacles on the same leaf was decidedly acid. With leaves excited by particles of glass placed on the central glands, the secretion which collects on the disc beneath them was much more strongly acid than that poured forth from the exterior tentacles, which were as yet only moderately inflected. When bits of albumen (and this is naturally alkaline), or bits of meat were placed on the disc, the secretion collected beneath them was likewise strongly acid. As raw meat * [In the ‘ Proceedings of the Royal ing secretion, and gives evidence that Society,’ 1886, No. 240, Gardiner has the secretion results from the break described the changes which go on in ing down of the protoplasmic reti« the glands of Drosera dichotoma dur- culum of the gland-cell.—F. D.]
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