270 THE GERM-PLASM 



are, however, also known in which these fluctuations are so 

 considerable as to become conspicuous. Sometimes, for in- 

 stance, the hybrid resembles one species as regards its leaves, 

 and the other with regard to its blossoms. Brandza* has 

 recently examined the general, as well as the microscopic 

 structure of certain hybrids, in order to ascertain the parental 

 characteristics exhibited by them, and has succeeded in proving 

 that a fluctuation of this kind exists. Marrubiiivi vaillantii^ a 

 cross between Leonunis cardiaca and Mamibiiuii vidgare^ for 

 instance, exhibited the winged leaf-stalk characteristic of M. 

 7'Hlgare, while the arrangement of the vascular bundles of the 

 petiole resembled that existing in Leomirits. The upper surface 

 of the petiole bore branched hairs like those of Leonurus^ while 

 on the lower surface the hairs resembled those of Marrubiuin. 



I shall speak of this fluctuation in the resemblance of the 

 organs to those of the parents as ' the shifting of the hereditary 

 residtants in ontogeny.'' 



We might imagine, a priori., that such a shifting cannot 

 possibly occur. If, as has been proved, transmission is virtually 

 completed at the time of fertilisation, and if therefore the 

 relative proportion of the two parental idioplasms is also fixed 

 for all the subsequent ontogenetic stages when they have once 

 been combined, we might expect a similar combination of the 

 characters of the parents to appear in all parts of the young 

 plant, so that these would either be exactly intermediate 

 between those of the two parents, or else that the paternal or 

 maternal characters would everywhere predominate in a similar 

 manner. The fact that this may not be, and in fact is usually 

 not the case, may be accounted for in several ways. 



In the first place, we must bear in mind the statement made 

 above, that a combination of two characters in equal proportions 

 need not always give rise to one which is apparently inter- 

 mediate, and that it is impossible to give an exact definition of 

 what is meant by such a character, because we only observe the 

 final eff"ect of forces acting within the cell, and not the actual 

 processes by which this eflfect is produced. This, however, 

 would not be a true shifting of the hereditary resultants, but 

 only an apparent one. 



Genuine cases of such a shifting, however, undoubtedly occur; 



* Brandza, ' Compt. rend.' 1890, T. Ill, p. 317. 



