lxii PROCEEDINGS—PERTHSHIRE SOCIETY OF NATURAL SCIENCE. 
on the other hand, are more southerly in their distribution, and less 
hardy in the conditions of habitat which they require for their proper 
development. 
In the trees which fringe our watercourses we see, as we might 
expect, a mingling of the two classes, the distribution being largely 
effected by the action of the stream itself in carrying down the seeds 
from one region to another and throwing them at random on its 
banks. 
I propose now, in conclusion, to glance at our woodlands at the 
different seasons of the year, noting particularly how each species has 
its own characteristic features by which it may be distinguished at 
any stage of its development. The annual cycle of change which 
takes place in our forest trees is, of course, familiar to all, but if we 
carefully note the progress of this cycle from month to month, or 
even from week to week, we shall find that it presents an infinitely 
greater variety of aspect than we were at first inclined to suspect. 
Let us begin with the middle of winter, when plant function is at 
its zero. The deciduous trees are all bare of leaves, save for a few 
shrivelled and russet leaves that still cling to the younger beeches 
and oaks. Scattered through the woods, however, are two native 
species that still give patches of green to remind us of the tints of 
summer, namely, the holly and the Scots fir, the berries of the former 
giving points of brilliancy in the winter landscape. Now is the time 
to study the wonderful symmetry of branching and the character of 
the bark in the different deciduous trees. These, we shall find, are 
quite as characteristic of the various species as are the forms of the 
leaves themselves. Take, for example, a few isolated trees standing 
in the fields by themselves, where we can view them against the sky 
line. The oak we can at once distinguish by its powerful lower 
limbs, going out nearly horizontally from the trunk, and by the 
general angularity of the branching. The beech, apart from the 
smoothness of its bark, can be distinguished by the way in which the 
main limbs all branch off from the bole at about the same distance 
from the ground, and at a very slight upward angle. The tapering 
of the branches, also, is gradual and regular. The ash is more 
elongated in general outline, and has its branches arranged in a series 
of alternate curves and angles, the twigs turning upward at the 
extremities. The elm is similar in outline to the ash, but the twigs 
stand out more abundantly from the main stem. The sycamore is 
rounded in outline, and generally flattened on the top. The lime 
has a symmetrical outline, the branching being at moderate angles 
and gradually diminishing in size. In the Spanish chestnut, on the 
other hand, the branches diverge at wide angles, and rapidly diminish 
in girth. Many other examples might be given, but these will suffice 
to show how completely each species has a character of its own to 
exhibit even in winter, when, to the casual observer, they are apt to 
lose their individuality. Even in colouring they differ from each 
other, as in the greyish tints of the beech, the silver of the birch, the 
orange brown of the plane, the dark umber of the oak, the paler 
brown of the ash, the red of the Scots fir, etc. To appreciate these 
