THE SEQUOIAS; THE SUNLIGHT AND THE SHADE
Wonderful sunlight effect, isn't it? We are here in Sequoia National Park and those big trees are sequoias, members of the pine-tree family.
[II. The March of the Trees]
Of course I don't mean to say it takes any 2,000 years for the average lichen to die and turn to dust. These long-lived lichens are the Methuselahs of their race. Most kinds die much younger, as time goes among the lichens, and in a comparatively few years, a century say, after their first settlement on the rock, the lichens have become soil. All this time the heating of the rock by day and the cooling off at night, the work of frost and the gases of the rain and the air[3] have also helped to make more soil and by and by there is enough for lichens of a larger growth; and mosses begin to get a foothold. These, in turn, die and, in decaying, make acids, as did the little lichens before them, and this acid joins hands with all the other forces to work up the rock into soil. Presently there is enough soil to let certain adventurers of the Weed family drop in. The picking is very thin, to be sure, but some of these Weed people have learned to put up with almost anything. Don't suppose, however, that all weeds are alike in this respect. Oh, dear, no! They come into new plant communities just as the trees do, not haphazard, but according to a certain more or less settled order. Some of them, the adventurer type, will, it is true, settle down and seem contented enough on land so poor that to quote the witty Lady Townshend "you will only find here and there a single blade of grass and two rabbits fighting for that"; while other weeds will have nothing to do with soil that, in their opinion, is not good enough for people of their family connections.
EARLY SETTLERS IN THE DESERT
Besides earning their own living under hard conditions, these sturdy pioneers of the desert are preparing the way for plants of a higher kind, as the next two pictures will tell you.