HEREDITY 381 



rating the two often passes through a flower or through a leaf (Braun, 185 i). 

 These segregations also claim our interest in that they are not confined to the 

 derivatives of individual cells, hut present themselves at the same time in many 

 cells (Beijerin'CK, 1901). The segregation in this case would therefore not be 

 directly connected with the division of the cells, and there must evidently be a 

 subsequent destruction of initials in the fully-formed cells. 



If initials, however, can disappear in a fully-formed cell it is possible that 

 they may also arise in them. We have every reason for treating this question 

 in connexion with C. adami. This plant, which passes for a hybrid, is said to 

 arise from the grafting of C. ptirpureus on C. laburnum. As, however, an ex- 

 perimental production of this graft hybrid, after its first fortuitous occurrence, 

 no longer succeeded, and as there appeared little probability of the formation of 

 graft hybrids in any case, their existence has latterly been denied (Vochting, 

 1892). The very definite statements of Kohne (1902) about a hybrid arising 

 from a grafting of Mespilus on Crataegus would appear to render this sceptical 

 point of view no longer quite justified. [According to Noll's (1905) most 

 recent statements it is scarcely possible to doubt that in this case we are dealing 

 with a genuine graft hybrid.] The hybrid twigs arise in this case at a certain 

 distance from the point of grafting, and it therefore appears quite impossible 

 that they could have arisen from cells which have grown together in the 

 process of grafting. [Noll considers that such a fusion of nuclei is self-apparent.] 

 It must rather be an effect produced by the Mespilus cells on distant Crataegus 

 cells. As Strasburger (1901 a) has found plasma bridges between graft and 

 scion, a migration of plasma particles, therefore, also of idioplasm, from the graft 

 into the scion is not impossible. No one, however, will wish to maintain that 

 cell-nuclei wander through these plasma bridges and unite with the nuclei of 

 other far distant cells, for the observations we owe to Miehe (1901) and KoR- 

 nicke (1901) regarding the wandering of nuclei from closed cells refer evidently 

 to pathological processes or artificial products. [In any case we must take 

 exception to Nemec's (1904) and Farmer's (1903) statements that a nucleus 

 which has migrated from one cell can fuse with another in a neighbouring 

 cell.] The graft hybrids pronounce distinctly against the exclusive allotment 

 of the idioplasm to either the nuclei or the chromosomes (compare, De Vries, 

 1903, for another interpretation of graft-hybrids [and Noll, 1905]), and we 

 may expect interesting lights on the question of heredity from a more exact 

 study of this kind of hybrid. 



Bibliography to Lecture XXIX. 



Beijerinck. 1901. Bot. Ztg. 59, 113. 



BovERi. 1902. Verhdl. d. Gesell. d. Naturforscher. Hamburg, 190 1, p. 44. 



[BovERi. 1904. Konstitution d. chromatischen Substanzen. Jena.] 



Braun, Alex. 185 i. Erscheinung d. Verjiingung i. d. Natur. 



Braun, Alex. 1857-9. Ueb. Parthenogenesis. (Abh. Berl. Akad.) 



BuRCK, W. 1900. Proc. Kon. Akad. v. Wetensch. Amsterdam. 



CoRRENS. 1899. Ber. d. bot. Gesell. 17, 410. 



CoRRENS. 1900 a. Ibid, 18, 158. 



CoRRENS. 1900 b. Bot. Ztg. 58, 229. 



CoRRENS. 1 90 1 a. Ber. d. bot. Gesell. 19, 71. 



CoRRENs. 1901b. Bibliotheca botan. 63. 



CORRENS. 1902. Bot. Ztg. 60, 65. 



CoRRENS. 1903. Ibid. 61, 113. 



[CoRRENS. 1905. Ueber Vererbungsgesetze. Berlin.] 



Darwin, i 876. Effects of Cross and Self-fertilisation. London. 



[Darwin. 1868. Das Variieren d. Pfianzen u. Tiere. Vol. II. 180. Leipzig.] 



[De Vries. 1903. Die Mutationstheorie. II. Leipzig.] 



[DiGBY. 1905. Proc. Roy. Soc, B. 76, 463.] 



Dixon. 1894. Annals of Botany, 8. 



Ernst. 1901. Flora, 88, ^7. 



