SQUINTING CUCUMBER.

1081

Fig. 19T.

mm

p ^ ont °rdica Elaterium.

StJlfe ex P e ^‘ n n its seeds.

a,ls verse section of the pepo.s\r

of which cohere, so as to form twobundles of two anthers each]. Fe-males : filaments three, sterile; ova-rium inferior, one-celled (spuriouslythree-celled); style simple ; stigmasthree, bifid. Pepo small, elliptical,pedunculated, grayish-green, coveredwith soft prickles; when ripe sepa-rating from its stalk, and expelling,with considerable violence, its brownseeds, and a thin mucus through theaperture at the insertion of the stalk.

The phenomenon of the expulsion of theseeds of this plant has acquired, of lateyears, increased interest, from the circum-stance of Dutrochet ( Nouv. Hech. sur VEnd.p. 66, 1828) having adduced it as one of theeffects of endosmosis. It is well known thatwhen two fluids of unequal density are se-parated from each other by membrane (ani-mal or vegetable), a double permeation offluids takes place,—that is, each fluid passesthrough the membrane, and mixes with theother fluid: the current in one direction iscalled endosmosis, that in the opposite direc-tion exosmosis. The instrument employedbyDutroi het in conducting his experimentshe called an endosmometer: it consists of abell shaped glass vessel (a bottomless bottle,for example), closed at the lower end bybladder, at the neck by a cork, through whichpasses a straight tube; or we may have acurved tube issuing from the side of the neck(as in Fig. 198).

' V 'U V P-R into the hell, and the bell then immersed in water, a portion of svrup"■ercuf - thr ' ‘ - ' - ■

-em-y . -'•“Ugh the bladder, while a larger quantity of water will pass in ; and if

f^hed p 6 P' ac ed in the curved portion of the tube (as in Fig. 198), the liquid metal is, s tronJS’ on the other hand, the bell contain water, and be immersed in syrup,® Ren er S ’i er .f urren t is from within outwards. In other words, the stronger current is,'^ttiesa i ° m the lighter towards the denser fluid. Hence we comprehend why*u plumbs shrivel w hen preserved in syrup, but remain plump in brandy: inthe first place exosmosis preponderates because the syrupis denser than the juice of the fruit,—in the second,endosmosis, because the juice is denser than the brandy:the separating membrane is, of course, the skin or epicarpof the fruit.

Now to apply these facts to the phenomena of the-Elaterium apple. In the centre of this fruit, and sur-rounding the seeds, is a very singular variety of organicmatter, which appears like thick mucus. It is called bysome botanists placentary matter (see Fig. 197, c). Moreexternal to this, that is, in the tissue of the pericarp, there-is another organic liquid, whose density is less than thatof the placentary matter. Now these two fluids beingseparated from each other by membrane, are in the exactcondition for the operation of endosmosis ; consequentlythe central cell gradually becomes very much distended(at the expense of the liquid in the tissue of the peri-carp), and ultimately gives way at the weakest point—namely, where the peduncle is articulated with the fruit,

' sr nometer.