Experimental Studies on the Variation 
of Yeast-cells 1 . 
BY 
EMIL CHR. HANSEN, Ph.D., 
Professor at the Carlsberg Laboratory , Copenhagen. 
I. 
I T was the epoch-making works of Darwin that gave the 
impulse to the tendency which is becoming more and 
more prevalent in modern zoology and botany, of viewing 
organisms from the standpoint of variation. As has been 
generally the case, the beginning was made here also with 
the higher organisms. Thus, the literature on phanerogamic 
plants abounds in observations in that direction ; the crypto- 
gams came under consideration considerably later, which is 
also true of yeast-cells and bacteria, or, as we usually style 
these two groups by a common appellation, micro-organisms. 
In the case of the Phanerogams, investigators have hitherto 
generally confined themselves to observations of the forms 
and phenomena as actually occurring in nature, and to dis- 
cussions on those observations. It is, however, evident that 
nothing short of systematic experiments, performed by exact 
methods, will be able to lead to a real insight into the very 
complicated problems of variation ; in this respect unicellular 
1 Read before the Botanical Section of the British Association, Ipswich, 
September 13, 1895. 
LAnnals of Botany, Vol. IX. No. XXXVI. December, 1895.] 
