124 REDUCTION OF VARIABILITY. 



admits of an explanation of the similarity between properties 

 of daughter-cells and mother-cells, as due to a quantitative pre- 

 ponderance of certain genes. This is a hypothesis somewhat sim- 

 ilar to the Weismann — Lamarckian one, with the exception 

 that it recognizes the fundamental difference between these 

 quantitative differences and the qualitative differences which 

 cause hereditary differences, the presence or absence of genes. 

 A group of organisms may become pure for a genotype which 

 causes them to possess some organ or peculiarity, which in 

 their present mode of life is absolutely useless. A number of 

 individuals out of this group may some day find themselves in 

 a position to which the same peculia ity tits them extremely 

 well. And it is often unnecessary to assume, that adaptative 

 characters were acquired under those conditions of life in 

 which they confer an advantage. We must remember, that there 

 is a perpetual broadcast distribution of seeds and young 

 animals. The seeds of the mistletoe will only develop on branches 

 of deciduous trees, and therefore only those seeds which 

 happen to be deposited upon such branches will have a chance 

 to develop. All the numerous seeds which fall to the ground or 

 which are deposited upon branches of conifers, or fence-posts 

 will perish. Probably the same proportion of the seed of Taxus 

 baccata is deposited upon branches of deciduous trees as that of 

 mistletoe. Some plants, like Sedum acre are adapted to a life 

 on walls. We are convinced that a much greater proportion of 

 dandelion seeds settle on top of walls than Sedum seeds. If, at 

 any day, a group of dandelion segregates out somewhere, which 

 is especially well adapted to a life on the top of the numerous 

 walls of France, this species will be found growing in those sit- 

 uations immediately. Plants and animals are continually 

 trying to fit themselves into all sorts of conditions, they are 

 continually hunting for a suitable place to live, and they 

 perish wholesale in the attempt. Dump a waggon-load of sterile 

 sand somewhere in Northern Europe. Carex arenaria will grow 

 on it almost directly. Sterilize a piece of moist bread, Asper- 

 gillus will be found growing on it within the week. Build a 



