the Nucleolus in Heredity . 273 
such ? reducing-division ’ occurs in the case of the higher 
plants at least h 
If then we are to look for reduction of the hereditary mass 
we are justified in searching for its elimination under some 
other form than the chromosomes. By assuming the location 
of some of the idioplasm or germinal substance in the nucleoli 
the nuclear processes during the development of the sexual 
cells become intelligible. During these processes in plants all 
observers agree that an extrusion of nucleolar substance 
occurs ; while in several cases a similar extrusion has been 
recorded during the formation of the polar bodies in animals 2 . 
Thus we may suppose that the redundant hereditary substance 
is extruded in the nucleoli during the development of the 
sexual cells, or, sometimes, by means of a reducing division 
of the chromatin (where such occurs), or by both. 
The fourth condition, with regard to the isotropism of pro- 
toplasm, affects Strasburger’s nuclear hypothesis and the 
proposed extension of it equally. It will be sufficient to refer 
to Hertwig’s discussion of it ( 1 . c., p. 354).; and to mention 
that Wilson, who accepts the nuclear hypothesis, does not 
completely endorse Hertwig’s view on this matter 3 . 
From the foregoing considerations it would appear that 
the proposed view regarding the hereditary functions of the 
1 Strasburger held for some time that in the first division of the mother-nucleus 
both transverse and longitudinal division occurred, and that no cleavage took 
place in the second division. He has since convinced himself that this does take 
place. Vide Strasburger and Mottier, Berichte d. Deutsch. Bot. Ges. 1897, p. 331. 
Since the appearance of this last paper of Strasburger’s, W. Belajeff has 
published a note (Ber. d. D. Bot. Ges., 1898, xvi. 2) in which he revives the 
opinion that no longitudinal cleavage of the chromosomes takes place in the 
second division of the pollen-mother-cells. It seems, however, as if his figure of 
this division Was taken from a later stage when longitudinal cleavage was com- 
plete. Indeed, I have little doubt, both from my own observations (vide On 
the Chromosomes of Lilium longiforuni , in Notes from the Bot. School, Trinity 
College, Dublin, 1896, Figs. 13 and 14) and from Strasburger’s and Mottier’s 
figures and results (quoted above), that longitudinal fission actually does occur 
in this karyokinesis. L. Guignard (Arch. d’Anat. Micro., 20 mars, 1899) also 
maintains that no longitudinal cleavage takes place in the second karyokinesis ; 
but it is not a ‘ reducing-division,’ inasmuch as a double longitudinal cleavage 
occurs in the first. 
2 Wilson, 1. c., p. 95, quoting Haecker. 3 Wilson, 1. c., p. 312 ff. 
