MUTATION. 165 



ter. And that there is independently from this, a mechanism 

 which makes the pollen of the young plant identical with that 

 of the father. Now, whatever the nature of this mechanism, it 

 pre-supposes at least, that in some way the two processes do not 

 interfere, just as the continuation of cell-division in the gener- 

 ations of Cytisus laburnum cells of a Cytisus adami tree does 

 not interfere with the genotype of the generations of C. Pur- 

 pureum cells in the inside. The characters of this graft-hybrid are 

 the result of a super-position of a layer of cells of one species 

 over tissues of the other species, but this something radically 

 different from real cooperation of genes derived from two species, 

 such as would take place in a real sexually produced hybrid be- 

 tween the two species. And in an analogous way, there may be a 

 great difference between real hybrids in Oenothera and the sort 

 of hybrids which show suspended segregation. But at the same 

 time we can conceive of a result of the cessation of the process 

 which is responsible for this suspended segregation, other than 

 the production of recessive novelties, namely the production of 

 dominant novelties, produced by combination of genes within 

 the cells. The male series of cells in a true-breeding Oenothera 

 may contain a gene A, and the female series of cells in the same 

 plant, and the same succession of plants may contain B. But it 

 is possible that these genes never meet in the same cells, so 

 that they do not cooperate in the way in which genes cooperate 

 which are present in one cell, and in many generations of 

 cells. Just as recessive novelties must be produced at any in- 

 terruption of the mysterious process which causes suspended 

 segregation in Oenothera, so can we conceive of combinations of 

 genes at the same time, combinations of genes which had been 

 present in the same plant but not in the same cells. 



It is very significant, we think, that the only instance of a 

 production of a dominant novelty in plants outside crossing is 

 the case recorded by Gates, the production of a red-fruited form 

 in one of these same Oenotheras which show the remarkable 

 true-breeding of hybrids. We would warn seriously against ac- 

 cepting such instances in this material as proving the spon- 



