HEREDITY 



379 



quality of regeneration. The later indirect nuclear divisions in the internodal 

 cells may possibly be the resttlt of the loss of capacity for regeneration, but could 

 never be its cause. Furthermore, Nathansohn (1900 b) has shown for Spirogvm 

 and Wasiliewski (1903) for Faba that by taking certain measures the typical 

 nuclear division may be transformed into the direct method without the cells 

 suffering any loss of function (compare p. 270). Besides this, there are plenty of 

 cells which are unable to exercise this or any function, e. g. regeneration, but 

 whose nuclei have nevertheless arisen in the normal manner. In a word, con- 

 clusive proof that the idioplasm is localized in the chromosome does not exist. 



But the chromosomes do not constitute the whole of the nucleus, and 

 perhaps the hereditary capacity lies in some other nuclear substance. The 

 supposition that the nucleus serves only as a receptacle for reserve material 

 connected with the hereditary substance must be entirely rejected, for in such 

 cases asSpirogyra it would be quite superfluous. If, however, other functions than 

 heredity be attributed to the nucleus, but if heredity is to be associated with it 

 only and not with the plasma, we have before us a view to which we must take 

 exception. This fact alone would appear conclusive, viz. that every male cell 

 bears protoplasm in addition to the nucleus, but it does not seem permissible to 

 placeavalueon its amount. Further, in the Phanerogams, Strasburger (1900 b), 

 himself an advocate of the ' nuclear theory ', has quite lately conceded the pas- 

 sage of protoplasm along with the male nucleus into the embryo-sac, although, 

 it is true, he points out that it is difficult to recognize it there. Guignard 

 (1900, 373) has also seen protoplasm pass from the male cell to the ovum. 



If BovERi's experiments were beyond criticism they would give extremely 

 strong support to the nuclear theory. Boveri fertilized the non-nucleate ova of 

 one sea-urchin with the sperms of another, and obtained hybrids showing 

 paternal qualities only. Unfortunately, grave exception has been taken to these 

 experiments (compare A. Meyer, 1902, p. 173). [Boveri, 1904, 105.] [God- 

 LEWSKi (1905) has advanced experimental proof that a sea-urchin egg deprived 

 of its nucleus may be fertilized by the sperm of A ntedon (one of the Crinoideae), 

 and that the organism resulting has the characters of the mother, whence it may 

 be concluded that cytoplasm without a nucleus is capable of transmitting 

 hereditary characters.] The question of the localization of the bearer of the 

 hereditary characters must for the present therefore be left undecided, or else 

 we must assume that this is to be soi^ht for just as much in the nucleus as in 

 the protoplasm, perhaps also in the chromatophores. Moreover, we are not only 

 ignorant where this substance is to be found, but we are equally in the dark as to 

 the way in which it operates. 



Having examined the distribution of the idioplasm in the cell, let us now 

 turn to its distribution in the plant as a whole. Here we find two sharply op- 

 posed views. One claims for the germ-cells (sex-cells and cells of growing points) 

 a very special role, they alone are said to be the bearers of the whole idioplasm ; 

 the other theory assumes the same potentialities to exist in any and every cell. 

 The first bases itself on the specialized phenomena in the animal world, the 

 other on similar phenomena in the vegetable world. In many animals the egg 

 by the first division is divided into two essentially different cells, one of which 

 is devoted to the construction of the whole soma, the other to the formation of 

 the sex-cells. The germ-cell, according to Weismann, contains the initials of 

 many organisms ; the somatic-cell of one only. By the further division of the 

 somatic-cells there arise the rudiments of individual somatic organs which only 

 develop further in this one direction. Weismann, therefore, assumes that 

 unequally inheritable divisions occur, so that, for instance, in one cell there are 

 only initials for the ectoderm, in another only those for the endoderm. Against 

 this view we may urge the behaviour of certain plants, notably Begonia and 

 Marchantia, in which undoubtedly from every cell, even when advanced in growth, 

 the whole organism can be reproduced by regeneration (p. 330), and in which, 



