110 JOUEXAL OF THE EOYAL HORTICULTUE-IL SOCIETY. 
which by clrying or by change of form may detach its numerous fruitlets 
at their bases, dry hygroscopic bract-scales forming the involucre, which 
are highly polished on their inner surfaces, and bristle-like pappus-hairs, 
which cannot be^called organs of flight like the feathery plumes of Thistle 
or Dandelion. In damp weather the pappus-bristles are pressed together, 
and the bract-scales close over; but in dry air both expand. ''Censer- 
action" of breeze or passing animal jerks the loose fruitlets up over 
the polished curve of the involucre, and its pappus-bristles, like the 
feathers in a shuttlecock, serve to determine the direction in which each 
fruitlet shall fall. Another closely similar series of comparatively slight 
adaptations is presented by the Labiate. Here we find a short but 
resilient pedicel to each flower ; a dry, persistent bell-shaped bilabiate 
calyx the curvature of the two lower sepals of which may determine the 
path of projection ; and a fruit which when ripe splits into four dry one- 
seeded nutlets. In some species of Teiicrium stiff, pliable converging 
hairs in the throat of the calyx have an action which has been compared 
to the rifling of a gun. A parallel but perhaps less specialised case is 
that of some species of Cerastium (Caryophyllaces) in which the S-like 
curvature of the capsule itself acts like the reflexed calyx teeth of the 
Labiata?, while the teeth of the capsule only recurve in dry weather, 
and the shortness of these teeth and ordinary " censer action," set up 
by gusts of winds or animals brushing past, economise the often abun- 
dant seed. 
Kerner describes yet another case of balistic action, which he defines 
as dependent solely on elasticity of stems and fruit-stalks, viz. that of 
Polygonum Virginicum, one of the Knot-grasses. Here there are strongly 
lignitied cells in the cortex of the short pedicel ; the capsule is jointed to 
the pedicel and is horizontal ; and the persistent style hangs vertically 
downwaiiis, ending in two divergent hooks. If these hooks catch in the 
hair of a passing animal the fruit will detach itself from its stalk as if 
from a watch-spring, whilst mere wind action will suflice to detach it, 
when it may be thrown two or three yards. 
We may perhaps class as a sort of appendix to the balistic group those 
fruits which creep or hop along the ground, though this action is 
essentially hygroscopic. It is in all cases dependent upon the presence 
of stiff hygroscopic bristle-like structures, though these bristles may be 
barbed awns, as in such grasses as JEgilops, Secede, and Elymus ; calyx- 
teeth, as in Trifoliu.m steUatum ; or parts of the pappus, as in the 
teazles and some Compositas. The most striking instance, perhaps, is 
that of the Barren Oat {Arena sterilis), in which the fruiting spikelet 
bears two awned glumes. The two awns twist hygroscopically in 
opposite directions, cross, and then slip apart with a jerk, making the 
whole spikelet jump up. 
Undoubtedly more complex are those adaptations which have been 
collectively termed " shng-fruits," in which the propelling force is due 
either to_turgor or to the drying up of certain parts of the fruit. Sub- 
dividing the latter into those cases in which the desiccation does not, 
and those cases in which it does, result in spiral torsion, we have three 
classes of sling-fruits. Of the first of these, that depending upon 
turgescen'je, the most celebrated example is that of the Squirting 
