Some Problems of Reproduction: a Comparative Study of ...

SOME PROBLEMS OF EEPRODUOTION. 65
ago. The one case which occurs to me, writing in Ireland,
is the Champion Potato, which proved the salvation of the
country after the great famine by its resistance to the
"blight" (Phytophthora vastatrix), but which after forty
years has now completely lost this resisting power. Again, we
have ample direct evidence for regarding the apparently "resting
" nucleus in a cell as having the same sort of relation to the
cytoplast as a nerve-centre has to an organism, 1 a view supported
too by the fact that the nucleus approximates in
chemical composition to nerve substance, being richer in
lecithin and phosphorus generally than the cytoplasm. Now,
in ordinary cell division, on the principle of continuity, there
is no essential chauge in brood-cytoplast and brood-nucleus,
and the result of repeated cell fission is merely a multiplication
of these. But we know that a nerve-centre ceases to
respond readily to a continued or repeated stimulus of the
same kind. It would seem then probable that, after a prolonged
association in life continued through a series of fissions,
the nucleus would respond less readily to the stimuli
received from the cytoplast; consequently its directive powers
would be diminished; and conversely the protoplasm would do
its work more imperfectly; the nucleus again would be less
nourished; and a vicious circle of deterioration would set up
in the cell, ending in senescence and death. Maupas has told
us that in the senescent Ciliata the cell-body is dwarfed and
deformed, the nuclear apparatus reduced and degenerated. 8
1 Cf. Haberland's researches on the behaviour of the nucleus in the activity
of the vegetable cell; Griiber's on artificial division of Ciliata; Eimer has
even adduced evidence to show that in nerve-centres themselves the nuclei of
the ganglion-cells play the part of primary centres (" The Cell-nucleus as
Central Nervous Organ," in 'Organic Evolution' [Bng. Trans.], p. 349).
" The recent researches of Fol (' Comptes Rendus, 1 April 20, 1891),
Guignard (' Comptes Rendus,' March 9 and May 11,1891), and Flemming
('Arch. f. mikr. Anat.,' t. xxxvii, pt. 2) complete the evidence that the "centrosome
" of Boveri plays an essential part in mitosis and karyogamy; and the
phrase "nucleus and centrosome" should in this section be used to replace
" nucleus" wherever it is used in antithesis to cytoplast in the present discussion.
VOJ,. XXXIII, PART I NEW SEE. E