Darwin's Pinigoirsis. 633 



definite material particles. These niulti])])- hy division 

 and at cell division pass on from the mother cell to llie 

 daughter cells (doctrine of pangenesis). 



Moreover all the cells of the body thrijw olf these 

 particles at various periods of their development. 'Ihese 

 reach the germ cells and hand over to them any char- 

 acters of the organism which they may lack (hypothesis 

 of transportation). 



The multiplication of the material vehicles of heredity 

 and their handing down, in the course of develojMiient. 

 b}^ the successive cellular and nuclear divisions, can be 

 most clearly seen in those cases in which certain vicarious 

 characters remain united during the greater part of tlie 

 development, and do not become separated until tlie cell 

 divisions have nearly come to an end. These units are 

 then seen to be distributed after the manner of a mosaic. 

 Macfarlane was the first to draw attention to this sig- 

 nificance of the phenomenon as seen in hvbrids ; and he 

 has shown, especially in Gcum hitcnncdiuin, how tlie 

 influences of both parents can remain combined in the 

 individual cells, or can be recognized as separating (mt 

 in these. Variegated leaves often show these late sepa- 

 rations very clearly,^ often in large areas of the most 

 widely different forms and shapes (Figs. 144 and 145). 

 or in small groups (Fig. 146).- But (nn* knmvledge 

 of a relation between these mosaic figures and develop- 

 ment is not yet sufficientlv complete to enable us to torni 

 a picture of these segregations of compound cliaracters 

 on the basis of the pedigrees*"' of the cells."* 



^A. J. J. VAN DER Velde. Auatomic en physiologic dcr hontr 

 hladcn, Handclingen, V. Vlaamsch Nat. en Gen. Congres. Rnigcs. 



Sept. TOOT. 



• Macfat^t,ane. On the Minute Structure, passim. 

 ■''See Intracellular Paui^cncsis (Fav^]. ed.). p. J^*^. 

 Mntcresting particulars liave been brought to ligbt by the recoiit 



