TIIK DISI'KRSAL OI- SEEDS. 
Ill 
Cucumber (Ecballiuin Elatcriuiii), in whicli one layer of cells in the 
pericarp of the bristly fruit is in a state of tension ; so that when the 
tissue round the apex of the fruit-stalk becomes disintegrated on 
ripening, the fruit is detached and its contents squirted out at the 
insertion of the peduncle. Some other cucurbitaceous species, such as 
CijclaiifJtera vxplodcns and TJdadiantJia duhia exhibit very similar 
phenomena. Equally well known is the adaptation of the Balsams, 
which has given them the generic name of Imjjatieiis, and our only 
British species the specific name Noli-mc-tancjerc, Touch-me-not. In 
this case the turgescent tissue is the mesocarp ; and w4ien the five 
coherent carpels of the fleshy capsule separate on ripening, or when a 
touch interferes with the balance of forces within, they roll themselves 
up violently inwards, hurling the seeds forcibly to a distance of some 
yards. As one walks through the woods near Lucerne one is bombarded 
by the seeds of this species, whilst the efficacy of this means of dispersal 
is evidenced by the widespread occurrence as w^eeds in our gardens and 
shrubberies of the Siberian species, I. ijarvi flora, D.C., and on our river- 
banks of the North American, I. fulva, Nutt. Very similar is the 
mechanism in the dry siliquas of various Crucifers of the genera 
Dentaria and Cardamine, especially C. impatiens, L., only that the 
valves of the siliqua roll outwards, and not, as in the Balsams, inwards. 
I have already alluded to the case oi Acantlius and other members of the 
order AcantJiacece, in which explosive capsules occur ; whilst the presence 
or shape of the " jaculators," or hook-like processes on the placenta 
which aid in the expulsion of the seeds, is sufficiently general to be used 
as a sub-ordinal character by the systematist. Another but very 
distinct case, in which a means of seed-dispersal seems certainly most 
efficacious, is that of the Wood-sorrels (Oxalis) and the allied genus 
Biophytum. Here the turgescent tissue is one of the inner layers of the 
seed-coat itself. The outer coat splits and is turned inside out, and the 
body of the seed is shot off to some distance. 
Omitting other interesting examples, if we pass to the second class of 
sling-fruits, those which act mainly by the drying up of certain layers of 
tissue, two well-known genera demand our attention from the slightly 
varied adaptations w^hich they possess, the Crane's-bills {Geranium) and 
the Violets. In Herb Robert {Geranium Bobertianum, L.) the outer 
tissue of the five awns or styles, the rod-like extremities of the five 
slightly coherent carpels, dries up and detaches the awai with a jerk from 
the central column or carpophore, throwing the seeds, according to 
Sir John Lubbock, sometimes more than twenty feet. In our British 
G. dissectum, L., in the Continental G. palustre, L., and other species, 
however, the carpels split along their under surfaces and the aw^ns bend 
outwards from below upward, so as to eject the seeds from inverted 
carpels, but do not themselves separate from the carpophore at their 
apices. Among Violets those species which have aerial stems, such as 
V. canina, V. tricolor, and V. elatior, have capsules w^hich split into 
three boat-shaped valves, each containing two rows of small polished 
seeds. The gradual drying up of the walls of these three valves squeezes 
out each seed in succession, one valve emptying itself before the second 
begins to do so. This pretty contrivance does not occur in the lower- 
