58 
PROCEEDINGS OP THE PERTHSHIRE SOCIETY OF NATURAL SCIENCE. 
not occupying the same spot as the parent. Moreover, I 
as they necessarily take the same substances from the soil, 
the struggle for existence is more severe between plants of 
the same species than between plants of different species, 
and this holds still more with the offspring of the same 
plant; hence it is of great advantage to the young plants 
to be scattered to some distance from one another. 
After these preliminary remarks, I shall now go on to 
notice some of the various adaptations that favour the dis¬ 
persion of seeds. These adaptations are frequently far more 
striking in exotic species than in any of our native plants, 
but I shall almost restrict myself to the latter, in the hope 
that it may excite the attention of some of you to what 
may be verified at home, and may induce you to enquiry 
into a subject that has been comparatively neglected 
among us. 
The agents in the dispersion of seeds are :— 
1. Wind, in many species. 
2. Water, in a few. 
3. Animals, almost solely quadrupeds or birds. They 
convey seeds, or one-seeded fruits, from place 
to place ( a) attached to hair or feathers by means 
of hooks, prickles, or sticky surfaces ; (6) they 
swallow the fruits, and the seeds are discharged 
uninjured from the intestines almost always at 
some distance from the place where they were 
swallowed. The seeds of plants growing in shal¬ 
low water and sinking into mud are often con¬ 
veyed, as pointed out by Darwin, on the feet of 
wading birds to considerable distances. But in 
this case there are no special adaptations of struc¬ 
ture necessary, so there is no need to refer to them 
at greater length. 
4. In some plants the seeds are thrown to some dis¬ 
tance by elastic dehiscence of the seed-vessel, e.g., 
in the broom, or of a seed-coat, as in the wood- 
sorrel. 
5. Movements may be effected by awns. 
Wind as an agent in dispersion .—One of the simplest 
and most general modes of utilising wind as an agent 
is seen in plants which bear the fruits supported on a 
stalk of some length, e.g., foxglove, poppy, hemlock, 
and many others. In most of such plants the fruit is 
dry, and splits open in some way or other to allow the 
escape of the seeds, which in such fruits are generally 
numerous and small. In these fruits the opening is almost 
always near the top, or if, as in the bluebell ( Campanula), 
it is near the base, the fruit usually hangs reversed. In 
this way the seeds are retained in it so long as it is at rest, 
but when the fruits and stems are driven about by wind 
the seeds are thrown to some distance around. In some 
plants, such as the hemlock, the fruits are one-seeded, and 
do not split open, but remain attached when ripe till 
jerked off when the plant is shaken by wind. Seeds of 
small size are carried off in the air, and are blown about like 
so much dust; and among cryptogams this is a very frequent 
mode of distribution, and the geographical range of these 
plants is often extremsly wide. Among phanerogams er 
flowering plants the seeds are seldom small enough for this, 
but they are frequently rendered sufficiently light by modi¬ 
fications of various kinds;—in their own structure if set 
free from the seed-vessel, or in the carpel or outer parts of 
the flower in the ase of one-seeded indehiscent carpels. 
In orchids generally, and here and there among other 
plants (e.g., Pyrola, Pamassia, Drosera Anglica, &c.) the 
seeds are verynumerous and small, and the outer coat of the 
the seed much wider than the inner, forming a loose bag 
filled only with air ; hence such seeds are very light and 
are easily blown about. 
A number of plants have the outer coat of the seed pro¬ 
longed to form a thin membranous wing, yielding the same 
advantage. In some (e.g., Spergidaria marginata and P.hin- 
anthus crista-galli), the wing surrounds the seed. No native 
Scottish plant has such a wing of large size, butin some tropi¬ 
cal species ( e.g.,Bignoniacece ) it reaches a breadth of over an 
inch. The firs and various other conifers have a large wing 
directed obliquely upwards and to one side; probably most 
persons have noticed how far these seeds are carried by 
even a moderate breeze before reaching the ground. The 
effect may also be understood if one examines moorlands 
or natural pastures for some distance around a fir wood. 
Young fir-trees will be found to be abundant in such 
localities, though cropped so close to the soil in pasturage 
that they need to be looked for. 
In other plants the seeds bear a coat of hairs over 
the surface (as in the cotton plant), but of this we 
have no conspicuous native example. Among willows 
and poplars, and also in tbe willow herbs ( Epilobium), 
each seed bears a tuft of hairs at one end, and the 
seeds themselves are small and light, so that they are 
wafted on by the faintest breeze. The dispersion of the 
seeds from a clump of willows or of poplars is often 
too noticeable to have been overlooked by even the least 
observant. 
Among one-seeded indehiscent carpels we meet with 
adaptations very similar to those just noticed among 
seeds, and also with others of a different nature, all 
serving the same use in the economy of the plant. Car¬ 
pels are frequently so like seeds in appearance that they 
are often called seeds (as in the so-called carraway seeds, 
