SPONTANEOUS CROSSING IN THE 
GARDEN BEAN, PHASEOLUS VULGARIS 
BY KARL B. KRISTOFFERSON 
LUND 

Si noie crossings are by no means rare in common garden 
beans, which every one knows, who has worked on the impro- 
vement of this species or used it for theoretical investigations. 
The estimates of the approximate percentage of the spontaneous 
crossing are, however, rather different. Some Swedish plant-breeders 
are of the opinion that it is probably quite inconsiderable, while others 
assume it to average up to 5 %. Even in the literature the statements 
are rather at variance. Thus Darwin considers it sometimes to be 
very great. FockE holds that it some years is very important, v. 
_TscHERMAK asserts that spontaneous hybrids now and then are found 
(FruwirtH 1910). Emerson (1916) has calculated the number of spon- 
taneous hybrids found in his cultures; it varied between 0 and 10 per 
cent. No attempts seem to have been made to ascertain the percen- 
tage by way of experiments. 
In my investigation I have made use of the following method. 
Small plots of the variety to be tested as to its tendency of cross-polli- 
nation were sown in the large field cultures of beans. These plots 
are here called »isolations». These were located at a distance of about 
20 metres from each other, and each plot contained only 5 or 6 beans. 
The field cultures of the bean were always put in rows, and the seeds of 
the isolations were sown in the rows (not between). As they ‘were 
put in the soil at the same time as the rest of the cultures the develop- 
ment of both sorts took place simultaneously. The time of flowering 
was also the same, a fact of great importance, of course. 
Thus every plant of the variety tested was quite surrounded by 
flowering plants of the large seed culture. As the number of the 
individuals in every plot was small, most of the crossings which re- 
sulted in the isolations must have taken place between plants of the 
isolation and the field culture beans, and only very few between plants 
belonging to the isolated variety. The percentage of spontaneous cros- 
sing should accordingly come very close to the maximal one. : 
Hereditas 11. 26 
