EFFECTS OF AMPHIMIXIS ON ONTOGENY 267 



the repetition and position of certain organs, and so on. Thus 

 the flower of Nicotiaiia paniciilata is decidedly longer than 

 that of N. nistica, and the former species is more extensively 

 branched and possesses a larger number of glands than the 

 latter. The above assumption that the individual determinants 

 correspond to one another in the two species cannot therefore 

 be quite an accurate one ; the germ-plasm of JV. panictilata 

 must, on the contrary, contain a larger number of determinants 

 than that of N'. nistica, and the process of disintegration of the 

 two species must differ in many ways. 



If an equal number of ids from each of these species occurs 

 in the hybrid, the two kinds of ids will only be able to co- 

 operate in ontogeny as long as their determinants still corre- 

 spond to one another. As soon as a point is reached in 

 which the ids of i\^. nistica begin to decline in number, and 

 their last determinants have become disintegrated, the ids of 

 N. panictilata will alone be able to produce series of cells ; but 

 as only half the normal number of these ids are present, the 

 structures arising from them cannot be as complete as they are 

 in the pure ancestral form : and, apart from this, the ids of 

 JV. nistica may possibly not have disappeared entirely, but the 

 succession of the determinants, which are, properly speaking, the 

 final ones, may persist beyond the normal period, and may in 

 this way interfere with the development of the pure characters of 

 A", paniciilata. This would, at any rate, render the fact com- 

 prehensible in principle that intermediate forms may also arise 

 in cases in which the struggle of the parental ids does not 

 extend into the final cells of ontogeny, and the characters of 

 the species come into contact at an earlier stage, as in the case 

 of the greater or less degree of ramification in plants. The 

 following considerations will make this more evident. 



In the second kind of combination, either the paternal or the 

 maternal characters predominate in all parts of the hybrid, so 

 that the latter bears a closer resemblance to one parent than 

 to the other : in this case, therefore, the transmission is appar- 

 ently monogonic. 



Several cases of this kind have been recorded, in some 

 of which the paternal, and in others the maternal characters 

 predominate. Instances of both kinds occur in the genus 

 Nicoiiana. "The hybrid Nicotiana paniciilata 9 x vinccvfloraZ 

 bears so close a resemblance to the last-named species that tlie 



