26o THE GF,R!VI -PLASM 



are probably contained in all the ids of the father as well as of 

 the mother, and the differences between the parents refer to 

 individual characters only. Our theoretical conception of the 

 idants as a collection of ids seems incompatible with the above- 

 mentioned statement that the child can only closely resemble 

 one parent, for only half of the idants of this parent take part in 

 the construction of the child. We shall, however, be able to 

 explain this apparent contradiction later on. 



The facts of the case may be stated in general terms as 

 follows. Half the number of parental idants always reach the 

 germ-cells of the offspring, but this half may consist of all 

 possible combinations of the parental idants : that is to say, 

 either of idants derived from the grandfather or grandmother 

 only, or of a combination derived from both, in which one or the 

 other may predominate. Nothing will be gained by taking the 

 ancestors of the third or fourth generation into consideration 

 until we come to consider the phenomena of reversion. 



3. The Struggle of the Ids in Ontogeny 

 a. Pla7it-Hybrids 



The structure of the offspring results from the struggle of all 

 the ids contained in the gerni-piasni. 



That this statement must be in general correct is to some 

 extent indicated by the fact that all parts of hybrid plants, pro- 

 duced by crossing two species or varieties, usually possess the 

 characters of both parents. The details concerning hybrids are 

 of far greater value for theoretical purposes than are those re- 

 lating to the normal offspring of any particular species, as we 

 know for certain that the characters which compete with one 

 another or combine, so as to result in the production of a hybrid, 

 must be contained /// every idant of one or other of the parents ; 

 for these characters are those of the species. 



The difference as regards the idioplasm between individual 

 and specific characters, seems to me to be due to the determi- 

 nants of the latter being present in an overwhelming majority in 

 all the ids of every idant of the germ-plasm, while the deter- 

 minants controlling the structure of individual characteristics 

 are only contained in a portion of the idants of which the germ- 

 plasm consists : at most they can only be present in all the 

 idants of one of the parents, — that is, in half the entire number 



