20 
A. E. GIBBS-SEEDS AND FRUITS J 
of the Surrey heaths have of late years been enclosed, and wherever 
this is the case young self-sown fir-trees have sprung up so closely 
together that there is not room for all to live. On the open heath 
there is not a single one. Why is it ? Simply because by fencing 
in the land the cattle have been kept from browsing. A search 
among the heath will reveal the stems of young firs that have been 
trying to grow and have failed, for as soon as they appeared they 
were eaten off by cattle. When the cattle are kept away, young 
fir-plantations spring up all over the place, the seeds being blown 
from some groups of trees on the neighbouring hills. The face of 
the country becomes changed from a barren heath to an extensive 
pine-forest. This instance shows the severity of the struggle going 
on, and how much influence unlooked-for agents exercise. 
The size and number of seeds produced by a plant are also im¬ 
portant factors. Minute seeds are more easily carried long dis¬ 
tances to spots suitable for germination than larger ones, and so it 
is often the case that rather large plants produce very tiny seeds, 
in immense quantities. The contents of the ripe capsule of the 
orchids resemble snuff, and Darwin has computed that the seeds 
may number 12,000,000. A single plant of Sinapis nigra has been 
known to yield 8,000 seeds, and a poppy, 60,000. 
The means adopted by some plants to disperse their seeds to 
secure the continuation of the species are very curious. In some 
cases the seeds are actually thrown considerable distances by the 
parent plant, as, for instance, in the broom and the little Cardamine 
hirsuta. In the violet family will be found a curious case in point. 
Of the three commoner species of Viola ( Tiirta, odorata, and canina), 
the dog-violet is by far the tallest and most free-growing plant. 
In the two shorter species, Tiirta and odorata , the fruit, when ripe, 
simply bends down to the ground and the capsule opens by three 
valves and allows the seeds to fall out. In the bigger dog-violet a 
very different action takes place. Here the seed-vessels, though 
pendant when young, elevate themselves and stand straight up 
when ripe, as those of the dandelion do, then the seed-vessel opens 
and the valves contract and curl inwards. Sir John Lubbock found 
that one gathered plant threw its seeds nearly ten feet. How we 
at once ask why the scented and hairy violets do not do the same 
thing. Tor this reason. They are short, almost stemless plants, 
and if they threw out their seeds they would simply strike against 
some neighbouring herbage and fall to the ground, so that no good 
end would be served, whereas the dog-violet is a taller plant and so 
stands above its neighbours and is enabled to throw its seeds over 
their heads. The wild geraniums also exhibit a curious set of 
movements for the dispersal of their seeds. 
Besides these plant-movements many other agencies are at work 
to distribute seeds. The wind plays a very important part, and 
to enable it to act there are many curious adaptations in some 
plants. In the poppy the fruit opens by pores at the top of the 
capsule just below the overhanging eaves. When the head is 
swung by the wind the seeds escape through these little doors. 
