Field and Woodland Plants

by William S. Furneaux

The recognition of the above facts introduces to us a difficulty for which we can find no explanation:—If the leaf-fall is not caused by frost, but by certain structural alterations that take place in the tree itself, how are we to account for the fact that the tree produces the changes which are necessary for its own preservation every year, just at the proper season? Plants and trees do not foresee the coming period of cold weather that necessitates the performance of the functions which they execute, and yet they instinctively prepare for the winter in the manner described above.

Our autumn observations teach us that there are interesting differences in the times and progress of leaf-fall of different species of trees, and also of trees of the same species when exposed to different external conditions. On open ground, where the trees are fully exposed both to the sun's rays and to the cool autumn breezes, the leaves lose their moisture and fall earlier than would the same species in more sheltered situations; and they retain their moisture and position latest in damp, shady woods. On high hills, where the exposure is extreme, the leaves, which, by the way, do not appear till late in the spring, fall early on account of the low temperature, and consequent decrease of root activity, in the autumn.

Further, we note that while in some trees, such as the Ash, Hornbeam, Beech and Hazel, the leaves fall first at the tips of the branches, and the defoliation extends fairly regularly towards the trunk, in other species, including Willows, Poplars, and the Lime, the branches become bare first at their bases, and finally at their tips.

Even during the depths of winter we may see a number of dead leaves still attached to the twigs of certain trees, notably the Oak and the Beech; but where we find practically all the foliage remaining on the tree or on special branches of a tree, we may generally assume that the tree, or the branches in question, are dead—that they died during the summer, before the separation layers of the leaves had been formed. We can also understand, from what has been said, why the dead leaves remain attached to a cut branch, and yet fall from the living tree from which it was severed.

In our own country some plants and trees retain their leaves throughout the year, so that we speak of them as evergreens. Many of these include herbaceous plants of a hardy nature, some of which remain fresh and green even in exposed situations, while others grow in more sheltered places. In either case they are plants whose roots remain more or less active in the cold season; and some of them, especially the evergreen shrubs, have rather thick leaves which contain a considerable quantity of sap, and which are surrounded by an outer covering or epidermis that does not allow the water within to pass out so readily as in the case of the deciduous leaves.

In addition to the observations previously mentioned, we should do well, at this season of the year, to study the autumn fruits of our trees and shrubs, most of which still remain attached to the twigs.

The Ash in Autumn, with its 'Keys.'

Some of these fruits lose most of their moisture as they ripen, thus becoming very light, and are provided with wings that cause them to be dispersed more or less by the wind.

The so-called 'keys' of the Ash are one-seeded fruits, extended at the end into a long, narrow wing with a slight twist. As a result of this peculiarity they usually fall less rapidly to the ground, spinning as they descend, and are thus carried farther than they otherwise would be by the wind. The fruits of the Sycamore and the Maple are somewhat similarly winged, and each of these consist of two carpels which separate sooner or later—generally after they have reached the ground.