we have seen, has also a leaf attached to the fruits, which answers the same purposes. Seeds of this character therefore occur on a large proportion of our forest-trees, and on them alone. But more than this: I have taken one or two of the most accessible works in which seeds are figured, for instance, Gärtner's "De Fructibus et Seminibus," Le Maout and Decaisne's (Hooker's translation) "Descriptive and Analytical Botany," and Baillon's "Histoire des Plantes." I find thirty genera, belonging to twenty-one different natural orders, figured as having seeds or fruits of this form. They are all trees or climbing shrubs, not one being a low herb.
Let us take another case, that of the plants in which the dispersion of the seeds is effected by means of hooks. Now, if the presence of these hooks was, so to say, accidental, and the dispersion merely a result, we should naturally expect to find some species with hooks in all classes of plants. They would occur, for instance, among trees and on water-plants. On the other hand, if they are developed that they might adhere to the skin of quadrupeds, then, having reference to the habits and size of our British mammals, it would be no advantage for a tree or for a water-plant to bear hooked seeds. Now, what are the facts? There are about thirty English species in which the dispersion of the seeds is effected by means of hooks, but not one of these is aquatic, nor is one of them more than four feet high. Nay, I might carry the thing further. We have a number of minute plants, which lie below the level at which seeds would be likely to be entangled in fur. Now, none of these, again, have hooked seeds or fruits. It would also seem, as Hildebrand has suggested, that in point of time, also, the appearance of the families of plants in which the fruits or seeds are provided with hooks coincided with that of the land mammalia.
Again, let us look at it from another point of view. Let us take our common forest-trees, shrubs, and tall, climbing—plants not, of course, a natural or botanical group, for they belong to a number of different orders, but a group characterized by attaining to a height of say over eight feet. We will in some cases only count genera; that is to say, we will count all the willows, for instance, as one. These trees and shrubs are plants with which you are all familiar, and are about thirty-three in number. Now, of these thirty-three no less than eighteen have edible fruits or seeds, such as the plum, apple, arbutus, holly, hazel, beech, and rose. Three have seeds which are provided with feathery hairs; and all the rest, namely, the lime, maple, ash, sycamore, elm, hop, birch, hornbeam, pine, and fir, are provided with a wing. Moreover, as will be seen by the following table, the lower trees and shrubs, such as the cornel, Guelder rose, rose, thorn, privet, elder, yew, and holly, have generally edible berries, much eaten by birds. The winged seeds or fruits characterize the great forest trees.