304 THE GERM-PLASM 



plane of section, the circle may be separated into nine dif- 

 ferent combinations of the black idants A of D. chinensis and 

 the white ones B of D. barbatus, viz. : 8A ; 7A + iB ; 6A + 2B ; 

 5A + 3B; 4A + 4B; 3A + 5B; 2A + 6B; 1A + 7B; and 8B. 

 Nine kinds of germ-cells, differing in quality, may therefore be 

 formed, the egg-cells only being taken into consideration in this 

 connection. 



In the formation of the so-called | hybrid, one of these egg- 

 cells unites with a germ-cell of the pure ancestral species B. 

 The following combinations of idants may then result : — 

 8B X SB, which would produce the pure ancestral species B 

 (7A+1B) 9 xSB ^ ; (6A + 2B) 9 x8B ^ ; (SA + 3B) 9 x8B^ 

 (4A + 4B) 9 x8B^ ; (3A + 5B) 9 x8B $ ; (2A + 6B) 9 x8B J 

 (1A + 7B) 9 X 8B ^ ; and 8A 9 x 8B ^ . Theoretically, therefore, 

 all stages from the pure ancestral form B (Fig. 22, III.) to 

 the form which is intermediate between the ancestral species 

 may occur, but no individual can arise which inclines more 

 strongly towards A than does the exactly intermediate form. 

 Whether all these are actually produced, and in what relative 

 frequency they occur, can only be decided by further researches 

 carried out from this point of view. Those which have till now 

 been made are insufficient, as the number of seedlings raised 

 has always been too small. We may, however, infer from the 

 facts we already possess, that the different combinations of the 

 two kinds of idants do not ocair with equal freqiieiicy, and that 

 the intermediate combinations are the most usual. Were this 

 not the case, ' the form which is intermediate between the \ 

 hybrid and the ancestral species ' could not be ' the most fre- 

 quent.' This is also most probable theoretically, and becomes 

 more so as the number of idants is greater. The cells of many 

 Phanerogams possess far more than sixteen idants, and even if 

 we also assume that the position of the line of section is entirely 

 a matter of chance, the rarest case will always be that in which 

 it accurately separates the idants of A from those of B, and it 

 will happen much more frequently that it divides them in some 

 other plane. This is equivalent to saying that germ-cells of 

 \ hybrids rarely contain idants of A or of B only, and that in 

 most cases there is a combination of the two. 



If the so-called f hybrids are again crossed with the ancestral 

 species B, I hybrids (the third hybridised generation) are 

 obtained, and these ' as a rule bear a close resemblance to that 



