By the end of summer, however, a transverse section of the bundle in question will show no actively-dividing constructive cells. The formation of new substances is over for the season, and each fibro-vascular bundle now seems to consist of but two important elements, wood-vessels and bast-tubes.
But the work of tissue-building in this kind of a bundle is not finished. It is merely arrested. The constructive life at the core is "scotched, not killed," and after remaining dormant all winter it reawakens in spring. Then a zone of young cells instinct with creative vigor will come into being between wood and bast, and tissue-building will recommence.
So the fibro-vascular bundles of roses and their kin are capable of renewing their growth, year after year, or, in technical language, they are "open".
In the country north of the Carolinas all native leaf-bearing trees are dicotyledons. In April, May, and June constructive tissue is present and active in them all. New wood is generated rapidly, and the vesels and cells which are formed are comparatively large. Later in the year, when life stirs less lustily in the vegetable creation, smaller vessels and cells will be formed. So the difference between "spring" and "summer' wood is often readily discernable even to the unaided eye, and always evident by aid of the pocket-lens.
We may see it on the upper surface of any casual stump. The spring wood often looks as if it had been used as a pincushion, because we see in it so many circular ends of now empty vessels and tubes. The summer wood is much more compact in its texture, and sometimes darker in color. So rings run around and around the stump, and by counting them we can tell the age of the tree - not accurately, but approximately. For it is quite possible that, if the season be moist, and the autumn late, more than one growth-ring will be formed in one year. If our stump were standing in Florida woods its rings would tell us little.
For there mild winters sometimes favor almost continuous growth, and cambium may be present, and new wood may be formed, during almost any month in the twelve. The rings of a tree (Fig. 28) are a trustworthy guide only in northern latitudes, where vegetation has a period of vigorous growth followed by a period of torpor.
In all dicotyledenous trunks the newest wood lies just beneath the inner bark, and the older wood toward the centre. So a little is added to the girth by each year's growth, till the enormously thick trunks of some or our larger forest-trees are built.
Fig. 28. - Crosswise section of the trunk of a young oak-tree, showing growth-rings. (From the Vegetable World).
The differences between the rose's kindred and the lily's kindred culminate in their flowers. The costly roses which droop in florist's windows are brought to an artificial state by arduous culture, and held in it by eternal vigilance. They are propogated mainly by cuttings. Left to themselves for a while their blossoms would dwindle and their pollen would intermix, till, in the course of time, the rose-garden would be filled with a generation of seedlings, showing what naturalists call "reversion to type." Jacqueminots, American Beauties, Bonsilenes and Catharine Mermels would be sought there in vain. In their stead we should find blossoms resembling some more, some less closely, the ancestral wild roses from which all sprang.
It is from the wild-rose, queen not yet come to her own (Fig. 29), that we shall best study the differences between the flowers of dicotyledons and those of monocotyledons.
The wild rose has five sepals and five petals. Its stamens are innumerable and the cells of the rose-hip are partially or entirely fused together. But the number five is more closely adhered to by other members of the rose tribe. The apple-blossom, for instance, has five sepals and five petals, and apple-seeds are stored in five horny pockets. The geranium tribe, the mallows, the numerous cousins of the pinks, the violets, almost every member of the immense buttercup connection, and many other blossoms of many tribes, follow the rule of five with more or less fidelity.
Fig. 29. - Wild roses.
Other large families among the rose's kin bear blossoms, whose parts, like those of the garden-fuchsia, are in fours or in multiples of four.
Among the lily's kin the parts of the flower are in threes, or their structure shows that they once followed the rule of three, which they have now partially abandoned.
The lilies themselves have three sepals and three petals, generally much alike in color and texture (Fig. 30). Sometimes all six have grown together into a chalice, which is still bordered with six reminiscent scallops.
Within these are three stamens - or, it may be six - forming an outer and an inner trio. At the flower's heart there may be three pistils, or, as in the flowering rush, six. or one, which, when we slice it across, is found to contain three seed-pockets. Sometimes as the seed-vessel ripens these pockets break away from one another, so that the final result looks almost like three ripened pistils (Fig. 31).
The palmettos of the Carolinas bear flowers much like those of grasses.
Fig. 30. - A lily-flower.
(From the Vegetable World).
Fig. 31. - Seed-vessel of the tulip. (From the Vegetable World).
And so we come to these . monocotyledons which, having diverged most widely from the primitive type, are most perplexing to the botanist, - the calla and her poor relations, and the cattail flags.