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POPULAR SCIENCE REVIEW. 
as is proved by their being traversed throughout their length 
by a fibro-vascular bundle containing spiral threads. Fig. 6 is 
copied from a drawing of "Warming’s, representing the internal 
structure of one of these organs. I am inclined to think, how- 
ever, from an examination of a number of leaves in a very early 
stage of development, that this is not the history of all the 
tentacles ; but that a number of them are true “ trichomes,” or 
epidermal structures. -That organs which closely resemble one 
another outwardly and perform similar functions, should not all 
have the same morphological origin, is not without parallel in 
the vegetable kingdom. The terminal glands are seen, when the 
plant is in a healthy and vigorous condition, to exude a quantity 
of a viscid secretion which can be drawn out into long threads ; 
and the quantity of this secretion is greatly increased by contact 
with organic matter. 
If an object capable of exciting the motion is placed in the 
centre of a leaf, the whole of the tentacles of the leaf gradu- 
ally converge towards it, and finally completely envelope it. 
If, on the contrary, the object is placed on one of the marginal 
glands, this tentacle only first of all bends over towards the 
centre of the leaf carrying the object with it; and then the 
same inflection occurs of the remaining leaves. The inflection 
takes place in the lowest portion of the pedicel only, the re- 
maining part of the pedicel and the gland itself remaining per- 
fectly straight. The exudation of the viscid secretion is how- 
ever from the gland only ; and Mr. Darwin records in his work 
some very remarkable facts connected with the change that 
takes place in the protoplasm contained in the various cells of 
the pedicel. In a leaf when in the normal condition, the cells 
of the pedicel are filled with a homogeneous purple fluid. This 
appearance undergoes a great change after the gland has been 
excited by repeated touches or by contact with an organic sub- 
stance. The cells have then a mottled appearance even to the 
naked eye, owing to the colouring matter becoming aggre- 
gated into purple masses of various shapes, which now float in 
an almost colourless fluid. This aggregation of the purple 
matter commences in the cells immediately beneath the gland, 
whence it travels down to the base of the pedicel ; the little 
coloured masses constantly changing their form, separating and 
reuniting with a motion similar to that of an Amoeba or of the 
white corpuscles of the blood. 
The aggregation of the protoplasm and the inflection of the 
tentacles are independent of one another, and are both brought 
about by a variety of causes — concussion of the gland, the pressure 
of solid particles of any kind, absorption of solid substances, and 
by a certain degree of heat. Any solid particle allowed to rest on 
a gland or a number of glands will produce inflection ; but if 
