A very similar arrangement is to be seen in the case of the goat’s-beard fruit and that of the coltsfoot, which, by reason of its flying device, secures a very wide distribution.
THE WILLOW ALSO PRODUCES
FLYING SEEDS
After flowering the Willow Herb develops long, pod-like processes. During damp and stormy weather these pods remain tightly closed. On a day when the air is dry and the breezes are light, the sides of the case split open and reveal a prodigious number of perfect flying machines. The seed itself weighs a mere trifle, and to this is attached a beautiful arrangement of feathery hairs. The whole thing is so well adapted for an aërial voyage that it mounts rapidly upward on the faintest puff of air. It should be here explained that by experiment it has been shown that the air currents tend to move upward. So light are some of these flying fruits that they often rise to an immense height. It is not an uncommon thing for them to be found on mountains thousands of feet above sea-level.
Of course, many foreign seeds have remarkable flying appendages. That of the South African Stapelia has a vast mass of fluffy hairs which will support it on quite a long aërial voyage. In the case of the cotton plant man has turned to good account the hairs by which the seed flies.
SEEDS OF THE SYCAMORE A DIFFERENT
TYPE OF FLYING MACHINE
In a large number of cases the conveyance of the seeds to a distant point is accomplished by the adoption of the screw-propeller principle. An excellent example of this is to be seen in the fruits of the sycamore. Here the actual seed is large and heavy, but it is attached to a wing-like expansion. When the fruit falls from the tree the wing revolves with great rapidity, very much on the lines of a propeller blade. This has the effect of controlling the rate of fall, so that the whole contrivance is carried to some distance before the seed is actually brought to earth.
PLANT TRAVELERS
ON LAND
Some kinds of touring plants send out long trailing stems to search for fresh rooting places. A little Alpine saxifrage is curious in this respect, for the plant will traverse over many feet of barren rock to reach a suitable position. Directly the shoot touches the soil, a new plant is formed, and as this grows up, the connection between it and the parent is severed. A kind of lily has an even more singular way of traveling about. Here, after the plant has flowered, buds arise on the stems which bore the blossoms. Eventually they take root in fresh positions. This plant if left alone would rapidly cover many yards with its offspring, and this without setting a single seed.
A strange group of plants are those which actually break themselves in pieces in order to pursue their journeys abroad. A plant belonging to the Houseleek order (Sempervivum soboliferum) is remarkable in this respect. The species naturally finds its home in the crevices of rocks, and at a certain stage in its development numerous little ball-like offshoots are produced. In the early days these are kept at home by the stems by means of which they are attached to the parent plant. Eventually these attachments shrivel up and the offshoots go rolling away over the rocks often much helped in their journey by the wind. A considerable distance may be traversed before a little ball finds a resting-place in some niche.