IN THE THEORY OF NATURAL SELECTION. 323 



developes into a flowering 1 shoot, produces at the same time the 

 germ-cells which are found in the latter. We thus approach an 

 understanding- of Fritz Miiller's observation ; for if the whole shoot 

 which produces the flower arises from the same idioplasm which 

 also forms its germ-cells, we can readily understand why the latter 

 should contain the same hereditary tendencies which were previously 

 expressed in the flower which produced them. The fact that varia- 

 tions may occur in a single shoot depends upon the changes 

 explained ahove, which occur in the idioplasm during the course 

 of its growth, as a result of the varying proportions in which the 

 ancestral idioplasms may be contained in it. 



Fritz Miiller's observation affords a beautiful confirmation of 

 this view, for if the flower itself transmitted the hexamerous 

 condition to its germ-cells, we could not understand why some of 

 the extremely rare hexamerous flowers were produced by the cross- 

 ing of two pentamerous flowers, in the control experiment. An 

 explanation of this fact can only be found in the assumption that 

 the germ-plasm contained in the mother plant, during its growth 

 and consequent distribution through all the branches of the colony, 

 became arranged into a combination of idioplasms, which, whenever 

 it predominated (as it did at certain places), necessarily led to the 

 formation of hexamerous flowers. I will not consider here the 

 question as to whether this combination is to be looked upon as an 

 instance of reversion, or whether it represents something new. Such 

 a question is of no importance for our present purpose ; but the 

 hexamerous flowers of the control experiment prove, in my opinion, 

 that germ -plasm containing the requisite combination was dis- 

 tributed in the mother plant and also existed, but in insufficient 

 amount, in shoots which did not produce any hexamerous flowers. 



APPENDIX V. ON THE ORIGIN OP PARTHENOGENESIS*. 



The transformation of heterogeny into pure parthenogenesis has 

 obviously been produced by other causes as well as by those mentioned 

 in the main part of this paper. Other and quite different circum- 

 stances have also had a share in its production. Pure parthenogenesis 

 may be produced without the intermediate condition of heterogeny. 



1 Appendix to page 290. 

 Y 2 



