. Evolution and its relation to religious thought . cias. In the former, the leavesare very finely bipinnate, and the general asj)ect of thefoliage is extremely feathery and graceful. In the latterthe leaves are simple, ovate, and, curiously enough, seton edge; and the general aspect of the tree is thereforerather stiff. It seems at first incredible that leaves sodifferent and asj)ects so diverse should belong to plantsof the same genus. But a little close examination showsthat, as usual, the botanists are right and the popularjudgment wrong. The plumose-leaf is the normal leaf-form for this g
. Evolution and its relation to religious thought . cias. In the former, the leavesare very finely bipinnate, and the general asj)ect of thefoliage is extremely feathery and graceful. In the latterthe leaves are simple, ovate, and, curiously enough, seton edge; and the general aspect of the tree is thereforerather stiff. It seems at first incredible that leaves sodifferent and asj)ects so diverse should belong to plantsof the same genus. But a little close examination showsthat, as usual, the botanists are right and the popularjudgment wrong. The plumose-leaf is the normal leaf-form for this genus. The simple leaf is not only abnor-mal, but in a homological sense is not a leaf at all—i. SPECIAL PEOOFS. 87 it does not correspond to the part called the hlade inordinary simple leaves of other trees. In the seedling ofthe simple-leaved acacias, and sometimes for a consider-able time in the young tree, the leaves are all the tree matures it gradually changes its dress andputs on its toga virilis. The gradual change from the. Fig. 3.—A branch of young acacia, showing change from one form ofleaf to the other; a, 6, c, (7, successive stages of change ; l^ s, leafstalk which gradually changes into the blade in c, </, and e. one form to the other may easily be traced in the sametree, and even often in the same branch (Fig. 3). The 88 EVIDENCES OF THE TRUTH OF EVOLUTION. steps of the change {a, h, c, and d) are shown in the fol-lowing figure, drawn from nature. It is seen, by bare in-spection of the figure, that the so-called leaf, d, of thesimple-leayed acacias, is really the yertically-expandedleaf-stalk, I, s, the true leaf or blade being wholly whole structure of this so-called leaf is differentfrom that of a true blade. Por example, its style of rib-bing is parallel, its position is edgewise to the sky, itspalisade cells are on both sides alike, etc. To empha-size this difference, botanists call such an apparent leaf apJiyUodium, or phyll
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Keywords: ., bookauthorlecontej, bookcentury1800, bookdecade1880, bookyear1888
