558 | 
Where the growth is colorless, not very dense and peculiar 
for the fineness of its meshes or radiations, it would be difficult 
to photograph the colonies by ordinary methods of exposure, 
since there is little difference in color between the medium and 
the object. 
A sensitive plate in an ordinary camera exposed to a plate 
culture by perpendicular rays of transmitted light shows little dif- 
ferentiation between the medium and colonies after development. 
The differentiation is also weak in the ground glass. 
When, however, the perpendicular rays of light are cut off, and 
oblique rays from several directions are thrown through the plate - 
culture upon the sensitive plate, the colonies are differentiated 
strongly in all their exquisite forms and tracings. The culture 
plates (Petrie dishes) or tubes, are inserted in an opening in the 
end of a box, which is painted perfectly black on the inside. 
Sliding boards, in a grooved frame, each cut to clamp over half 
the Petrie dish and lined with black velvety stuff hold the plate 
culture in position. The lens of the camera is pointed toward a 
window with the plate culture between. A perfectly black screen, 
30 cm. to 40 cm. in diameter is then hung upon the window 
directly in front of the object in order to cut off the perpendicular 
rays of light. 
BOTANICAL DEPARTMENT, CORNELL UNIVERSITY. 
Crossing of Cucurbits.* 
By L. H. PAMMEL. 
So widespread is the popular belief that. several members of 
the genera Cucurbita, Cucumis and Citrullus will hybridize and 
“mix,” that it is difficult to convince people of these errors. 
What is more surprising is that these opinions should find support 
among a certain class of popular scientists. It is scarcely neces- 
sary to repeat experiments of this kind, after the diligent work of 
Naudin, Bailey, Munson and others who have all demonstrated 
Seas cae | 
* Read by title before -the Section of Botany, A. A. A. S., Madison Meeting, 
August, 1893. ee 
