CARNIVOROUS PLANTS. 
359 
The genus Pinguicula belongs to a natural order widely sepa- 
rated from Drosera. The Butterworts are all, like the sundews, 
natives of bogs, and are so called from the greasy texture of the 
thick leaves, caused by the viscid glands with which the upper 
side of the leaf is studded. The commonest species, P. vulga- 
ris , fig. 8, is a very familiar plant by the side of streams and in 
other wet places in all the mountainous districts of our islands ; 
but its deep blue flowers have passed away by the middle of 
summer. A second species or sub-species, P. grandiflora , with 
much larger blue flowers, is confined to the south-west of 
Ireland ; and P. alpina , with nearly white flowers, to the most 
alpine parts of Scotland ; while the fourth British species, 
P. lusitanica , with small lilac-yellow flowers, is abundant in the 
south-west of England, and the west of Scotland and Ireland. 
The contrivance for capturing insects is very different in the 
case of Pinguicula to that which we have described in Drosera. 
The whole of the upper surface of the leaf is studded with a 
number of glands composed of a stalk or pedicel, which consists 
of a single cell, and of a flat capitate head, formed of a number 
of small cells, usually eight or sixteen ; their mode of growth 
is represented in fig. 9, magnified ; and a single one on a much 
larger scale in fig. 10. They are always secreting a large 
quantity of an extremely viscid fluid, neutral to test-paper ; but 
have no power of motion when excited ; the only movement in 
the leaf of the butterwort being a very slow incurving of the 
margin over any imprisoned object. The extreme viscidity of 
the secretion from the glands is the sole means by which the 
entrapped animals are detained. The incurving of the margin 
is caused either by the pressure of any solid particle, or by con- 
tact with a digestible substance, whether solid or in solution ; 
but after a comparatively short time the margin again unfolds. 
The general results of Mr. Darwin’s observations on Pingui- 
cula vulgaris amount to this : — Objects not containing soluble 
matter have little or no power of exciting the glands to in- 
creased secretion; while dense nitrogenous fluids cause the 
glands to pour forth a large supply of viscid fluid, which is still 
not acid. On the other hand the secretion from glands excited 
by contact with nitrogenous solids or liquids is not only very 
copious, but is invariably acid. The secretion in this state has 
the power of rapidly dissolving and digesting the tender part of 
the bodies of insects, meat, cartilage, albumen, fibrin, gelatine, 
and caseine. The secretion which has absorbed nitrogenous 
matter is quickly re-absorbed by the glands, which change their 
colour from green to brownish, and contain masses of aggregated 
granular, presumably protoplasmic matter, while no such effect 
is produced by the action of non-nitrogenous fluids. 
The phenomena exhibited by the butterwort have not, how- 
