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The disease is "contagious," because a healthy fly coming in contact with a diseased one, from which the spore-bearing filaments protrude, is pretty sure to carry off a spore or two. It is "infectious" because the spores become scattered about all sorts of matter in the neighbourhood of the slain flies.
These primordial germs, or the ZRA of the Bible genesis, must have preceded the first fungous growth, as they preceded the first spore-bearing cryptogam.
The plants of this period are not the plants of to-day, though we still have some very degenerate representatives of them. The common horse-tail, with its angular, slender, leaflike branches and its club-shaped spore-bearing body, is a modern degenerate descendant of the treelike calamites of the Carboniferous forest.
It affects the tomato as it does the potato, forming on the leaves dark, discolored spots, which spread rapidly under favorable conditions, killing the foliage in a few days. The fruit is also attacked and becomes covered with the mildew-like spore-bearing threads of the fungus. Bordeaux mixture properly applied is an efficient preventive.
The botanist finds even more difficulty than the zoologist in drawing up the pedigrees of his plants, but the general features of the larger groups which he finds in succession in the chronicle of the earth point very decisively to evolution. The seed-bearing ferns of the Coal-forest point upward to the later stage, and downward to a common origin with the ordinary spore-bearing ferns.
Such a branch-system is called an inflorescence. The primary function of the flower is to bear the spores. The flower may consist only of spore-bearing leaves, as in willow, where each flower comprises only a few stamens or two carpels.
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