Berries are the favorite food of many of our native mammals, the woodchuck and others. Wild apples are frequently carried off by squirrels, and it is well known that squirrels store up large quantities of nuts which oftentimes are never eaten. Fruits too large to be swallowed by most birds are easily devoured by the larger mammals, the apple, for instance, whose seeds are protected by tight husks well adapted to slip through the alimentary canal of an animal without receiving the least injury.
The gourd fruits, so much liked by man here, are equally attractive to his quadrumanal brothers in the tropics.
For utilizing the services particularly of mammals many fruits have developed hooks or horns to catch in the fleece of passing creatures, who thus transport the seeds from place to place. An autumn tramp through our pastures will soon convince one of the efficiency of this mode of dissemination.
A very familiar example of this kind we find in the common burdock; but the hooks of the burdock are insignificant affairs compared with some which exist. In the Southern States grows a fruit, Martynia proboscidea, having two recurving horns several inches long. The appearance of the fruit would justify its having an even more formidable name. Another fruit, Harpagophyton by name, is a bristling mass of powerful hooks. It is said that lions trying to free themselves from its clutches get it into the mouth and die in torture. Instead of hooks, seeds sometimes effect the same purpose by being sticky.
It is a suggestive fact that hooked fruits occur on low plants, never on trees; also that in geologic time hooks appeared simultaneously with land mammals.
Lastly, we must recollect that man himself disseminates seeds in a thousand ways. War often introduces new plants into a region. Commerce is of vast importance in this respect. In the vicinity of our woolen mills a strange flora, from seeds introduced with the raw wool, is struggling with native plants. Agriculture is certainly of unbounded effect in the way we are considering. In short, human will has almost limitless control over the circumstances of plant life.
After dispersion most seeds simply rest on the ground to await germination, perhaps protected by color resemblance, as in nuts, or by mimicry, sometimes mimicking a dry twig to perfection. Some seeds, though, do more than this. The parasitic seeds of the mistletoe, dropped by birds on the boughs of trees, would soon fall to the ground and die were they were not very sticky. The seed of Mysodendron has three long, flexible appendages which twine round any suitable branch to which it is blown.