130 Bulletin Wisconsin Natural History Society. [Vol. 6, Nos. 3-4. 
Milwaukee, April 30, 1908. 
Regular monthly meeting' of the society. 
President Teller in the chair and fifty persons present. 
The minutes of the reg-ular March meeting- and those of the sec- 
tion meeting in April were read and approved. There being- no opposi- 
tion, the chair appointed Messrs. Fing-er, Monroe, Russel, and Graeni- 
cher as a committee to take charge of and organize the work in connec- 
tion with preparing a check list of the flora of Wisconsin in accordance 
with the recommendations of the sections. 
The name of Dr. Rudolph C. Gruettner, 271, 22nd Ave., City was 
presented by Dr. Barth for membership and subsequently was favorably 
acted upon by the directors. 
President Teller then introduced the speaker of the evening, 
Professor W. L. Tower of the University of Chicago, who spoke on 
"Variation, the Basic Phenomenon in Organic Evolution." Professor 
Tower gave a short sketch of the history of evolution, the attitude of 
religion and philosophj'- to this doctrine and its passage from a deduc- 
tive to an inductive study. Variation was early recognized as being 
the important factor in evolution and Bacon first recognized that there 
were two kinds of variation, an ordinarj^ or fluctuating one and an 
extreme or saltatorj^ variation producing mutants. 
The speaker made the distinction between somatic and germinal 
variation or that which is tranmitted to offspring. Under this latter 
class came certain experiments of his in which he found in breeding 
200,000 or more beetles of the genus Leptinotarsus that the offspring 
belonged to one series only and not to a Mendelian group; and another 
in which A crossed with C produced only A and C or A or C onl3^ He 
called attention to the fact that what sometimes appears to be the 
inheritance of disease is in reality due to intrauterine infection. 
He explained the peculiarities of oviposition of Leptinotarkus in 
lying a mass of eggs at one time, followed by a period during 
which no eggs are laid, a phenomenon repeated several times and which 
is convenient for the experimentor as it enables him to select any one 
or more of these egg-lying periods for subjecting the female to stimuli 
of temperature and humidity, reserving the products of other periods 
as checks upon the results. 
The beetles if subjected to stimuli of temperature and humidity 
at ordinar;;^ times develop certain definite characters that are not trans- 
missible ; but if these stimuli are applied at the time of the fertilization 
of the ova, the resulting variation is then inherited, continuing' without 
change for many generations. The speaker referred to experiments 
made by MacDougal on plants. In these he injected salts of Zinc, Cal- 
