116 
PHYSICS: A. F. BLAKESLEE 
Proc. N. A. S. 
The value of 0 could be determined from an X-ray photograph of a 
mercury meniscus in a capillary composed of the material under exam- 
ination, or by the drop-shape method. 
AN APPARENT CASE OF NON-MENDELIAN INHERITANCE 
IN DATURA DUE TO A DISEASE 
By Albert F. Blakeslee 
Station for Experimental Evolution, Cold Spring Harbor, N. Y. 
Communicated by C. B. Davenport, February 26, 1921 
In the common Jimson Weed (Datura Stramonium), spiny or armed 
capsules are dominant to smooth or inermis capsules. A cross between 
two plants, each homozygous for a single member of this pair of characters 
will produce spiny fruited offspring in the Fi and a ratio of 3 spiny to 1 
smooth plant in the F2 generation. 
In 1915, the writer found a single inermis plant in a culture where smooth 
capsules could not have occurred through segregation. It was considered 
a new inermis mutation and its inheritance was therefore studied in crosses 
with normals. 
The new form was called Quercina on account of the increased oak-like 
dentation of its leaves. The most conspicuous character on the mature 
plant was the partial or complete suppression of spines on the capsules. 
An examination of the plants throughout the growing and flowering con- 
dition indicated that other parts of the plant were also involved and 
showed such changes as the slitting of the normally undivided corolla, 
the absence of pollen, which caused the plant to depend upon outcrossing 
in order to set seed, and certain other characters associated with less 
vigorous growth. 
Later investigation showed that the Quercina character occurred spon- 
taneously in the garden cultures in many ways like a vegetative mutation. 
In a single year's test, about 1V4 per cent of the normal plants in the field 
took on the Quercina character by the last of the season. This Quercina 
character generally shows itself weakly in a single branch and gradually 
spreads to all the new growth. It occasionally happens on plants which 
are acquiring the Quercina character that capsules will be found in a 
transitional condition with their spines only partially reduced. Some- 
times some of the valves may be entirely smooth and others on the same 
capsule fully spined. 
So far as we can judge from the literature, other investigators who^have 
worked on the Jimson Weed found have Quercina plants in their cultures. 
They seem not to have noticed, however, any of the distinctive characters 
other than those shown by the capsules. 
