WICnURA ON HYBRIDS. 



79 



individual from which it was taken, and each of the two species 

 gives to the new structure a numerically equal part, namely one 

 cell. Both united in opposite crossing must give the same inter- 

 mediate form, in which both species have entered in equal pro- 

 portions. 



4. Embryo- cells and pollen-tubes give exclusively the subse- 

 quent peculiarities to the product in consequence of their con- 

 taining within them the type. The relation of the mother plant 

 to the embryo after the completion of impregnation is that of the 

 stock to the graft. Both nourish a strange individual, and are 

 intimately connected with it, without exercising any influence 

 whatever on its typical peculiarities. 



5. If the remaining cells, on their growth into branches, repro- 

 duce as a rule the same individual of which they are the essential 

 part, experience teaches, on the contrary, that in the process of 

 production many individuals of abnormal structure — that is, 

 varieties — make their appearance. 



6. Since the sexual union of differently constituted individuals 

 (that is, hybridizing) always produces a being intermediate between 

 the type contained in the ovule and that in the pollen-tube, we 

 may regard it as a law which has equal weight in the origination 

 of varieties. 



7. The existence of a variety is therefore a proof that the ovule 

 or pollen-tube from whence it sprung, or both, must have had a 

 type departing from that of the normal species. 



8. The embryo-cells and pollen-tubes have therefore not merely 

 the function of reproducing the individual, but also of new ab- 

 normal forms. 



9. In hybrids the power of forming varieties exists especially 

 in the pollen, in a less degree in che ovules ; and this is probably 

 also the case in pure species. 



10. If we reflect that the new individual arising from impreg- 

 nation is intermediate between the type of the pollen of the male 

 and the embryo-cell of the female, we must, in order to explain the 

 form of the variety, assign to the variety-producing sexual cells a 

 tolerably wide departure from the ancestral type. 



11. If a variety-forming ovule combines with a variety from 

 pollen-grain, so abnormal a form may arise from the union that 

 we may perhaps explain in this way the origin of Gsertner's ex- 

 ceptional types, assuming the correctness of his observation. 



12. It is doubtful whether the variety-forming power of the 

 pollen can be seen from outward inspection ; this certainly is not 



