92 PROCEEDINGS OF THE 



chromosomes. This is a well-kaovvii phenomenon among \Yild 

 species, and 30 or 40 such cases are now known. There is every 

 reason to suppos^e that tetraploidy has originated in these cases 

 as it lias in (E. gigns. In this mutant, wherever the douUing of 

 chromosomes occurred in the life-cycle, it obviously took place 

 suddenly in a single cell. Whether this was before or after 

 fertilization is a detail, but the accompanying increase in the 

 size of the cells and nuclei alone accounts for most of the 

 peculiarities of gigns, even such as the short fruits and the in- 

 creased susceptibility to frost. 



Instead of this view, based on the cytological facts. Dr. Lotsy 

 offers a theory of purely hypothetical genes, which no one has 

 ever seen and which may not exist at all. He begins by as- 

 suming tfiat (E. Lamarchiana is a heterozygote in the Mendelian 

 sense. This is a pure assumption, and the numerous crossing 

 experiments of de Vries show clearly that his race was not 

 heterozygous in the Mendehan sense. Is it not obvious that the 

 cvtological facts furnish a useful check on unbridled speculation 

 about hypothetical genes ? 



There are many other criticisms \^liich might be made, but I 

 will only recall to your minds the fact that there are mai^y well- 

 authenticated instances of mutation in the Bacteria. If muta- 

 tions can occur in bacteria iu the absence of crossing, why not in 

 higher plants ? 



Dr. Keeble urged, in opposition to the views expressed by the 

 previous speaker (Dr. Gates), that the members of lines of 

 plants which are homozygous for a considerable nuinber of Men- 

 delian factors are remarkably uniform and stable. For example, 

 in his experiments with peas {Pisum sativum) he had bred races 

 which grew at the same rate, reached equal heights, flowered at 

 the same node and at the same time. Hence, it may be conceded 

 that pure lines are very stable, although the evidence available at 

 present does not allow of the claim that no variation occurs among 

 the members of a pure line. The cytological evidence brought 

 for^v^ard hj Dr. Gates may concei\ ably be read in either way — for 

 example, a giant form may be gigantic because it has double the 

 number of chromosomes possessed by the ordinary form from 

 which the giant arose, or it may have the double number of 

 chromosomes because it is a giant. 



Professor Dendt expressed the opinion that the development 

 of organisms, whether phylogenetic or ontogenetic, was a dual 

 process. There was, first, what might be called the fundamental 

 development, which might be compared to the main theme of a 

 piece of music ; and, second, a series of features superposed upon 

 the fundamental development, which might be compared to varia- 

 tions on the main theme, and which were due to crossing or 

 hybridization. He asked his hearers to try to work out for 



