The Principles of Biology, Volume 1 (of 2)Spencer, Herbert
Science
The Principles of Biology, Volume 1 (of 2)
Spencer, Herbert
Biology
Already in § 77 I have illustrated the power which some plants possess of
developing new individuals from mere fragments of leaves and even from
detached scales. Striking as are the facts there instanced, they are
scarcely more significant than some which are familiar. The formation of
cauline buds, presently growing into shoots, shows us a kind of inheritance
which a true theory must explain. As described by Kerner, such buds arise
in Pimpernel, Toad-flax, etc., below the seed-leaves, even while yet there
are no axils in which buds usually grow; and in many plants they arise from
intermediate places on the stem: that is, without definite relations to
pre-existing structures. How fortuitous is their origin is shown when a
branch is induced to bud by keeping it wrapped round with a wet cloth. Even
still better proved is the absence of any relation between cauline buds and
normal germs by the frequent growth of them out of "callus"--the tissue
which spreads over wounds and the cut ends of branches. It is not easy to
reconcile these facts with Mr. Darwin's hypothesis of gemmules. We have to
assume that where a cauline bud emerges there are present in due
proportions gemmules of all the parts which will presently arise from
it--leaves, stipules, bracts, petals, stamens, anthers, etc. We have to
assume this though, at the time the bud originates, sundry of these organs,
as the parts of flowers, do not exist on the plant or tree. And we have to
assume that the gemmules of such parts are duly provided in a portion of
adventitious callus, far away from the normal places of fructification.
Moreover, the resulting shoot may or may not produce all the parts which
the gemmules represent; and when, perhaps after years, flowers are produced
on its side shoots, there must exist at each point the needful proportion
of the required gemmules; though there have been no cells continually
giving them off.
Still less does the hypothesis of Prof. Weismann harmonize with the
evidence as plants display it. Plant-embryogeny yields no sign of
separation between germ-plasm and soma-plasm; and, indeed, the absence of
such separation is admitted. After instancing cases among certain of the
lower animals, in which no differentiation of the two arises in the first
generation resulting from a fertilized ovum, Prof. Weismann continues:--
"The same is true as regards the higher plants, in which the first shoot
arising from the seed never contains germ-cells, or even cells which
subsequently become differentiated into germ cells. In all these
last-mentioned cases the germ-cells are not present in the first person
arising by embryogeny as special cells, but are only formed in much later
cell-generations from the offspring of certain cells of which this first
person was composed." (_Germ-Plasm_, p. 185.)
Public-domain text, read in full here on John Shaqi.
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