Another means of dispersal is not so obvious on the South Downs. In the Arctic region a glacier breaks away at its tongue into icebergs, which float off and are stranded somewhere perhaps hundreds of miles distant. Upon these icebergs are stones and soil and plants which may be carried to a great distance from their original place. In the Glacial period or Great Ice Age, ice may have been an important help in distributing plants, but at present it is difficult to find a good example.
From all this it is clear that in order to carry plants to new countries and new homes, everything that moves on the earth's surface can be employed. Not only the wind, but ocean currents, river waters, icebergs, and floating ice are used. Migrating birds, mammals, and especially the most restless and unsettled animal of all, viz. man, are at work consciously and deliberately, or unconsciously and accidentally, carrying the seeds to form new forest, grasslands, or harvests in other countries.
The subject is in truth so vast that it is difficult to select the most interesting and important cases.
The way in which squirrels, rats, voles, and lemmings devour nuts and the like often leads to the distribution of the fruit. A squirrel may, like a human being, forget where its store was buried, or be driven from the place. Then some of those forgotten nuts will grow into trees.
Birds are known to travel enormous distances. It is said that one little Arctic bird travels from Heligoland to Morocco in a single flight. It would not, at first sight, seem likely that seeds and fruits could be carried by birds; yet Darwin saw that this might possibly be the case. The mud and slime in which so many birds find the small insects which they require is full of seeds. An Austrian botanist, Kerner von Marilaun, examined the mud scraped from the beaks, feathers, and legs of a number of wading and marsh-birds. He found in it the seeds of no less than thirty-one different water and marsh plants (Grasses, Sedges, Toad-rush, etc.). This showed, as is very often the case, that Darwin was the first to discover a very important point. It is also interesting to find that these ugly little freshwater mud and marsh plants are at home almost everywhere, from the Arctic circle to Tierra del Fuego and from Peru to Japan.
The most extraordinary cases known of sticking fruits and spines are the Martynias and Harpagophytons of South Africa. The fruit is covered by hooked claws, and becomes a regular pest wherever it occurs. Deer, antelopes, and other animals get their hoofs entangled in the fruit, and the wretched creatures have to limp about until the hard thorny fruit is trodden to pieces. Dr. Livingstone says that the fruit gets into the nostrils of grazing animals which cannot possibly remove it themselves, and so have to wait patiently till the herdsman comes to take it out. According to Lord Avebury, lions may sometimes be destroyed by these horrible fruits. When a lion is rolling on the sand, the claws (an inch long) stick in his skin, and when the lion tries to tear it away with his teeth his mouth gets full of the fruits and he cannot eat, and perishes miserably of starvation.[115]
Stereo Copyright, Underwood & UnderwoodLondon and New York
A Cocoanut Grove in Ceylon