FEBRUARY 15, 1901.] 
color could not be due to sulphur granules, 
as has been supposed,—neither was it pos- 
sible to demonstrate any definite coloring 
matter within the cell itself. Numerous 
experiments with  Oscillatoria prolifica, 
Gorn., a plant particularly favorable for 
study, showed that the red color must be 
caused by the refraction due to the presence 
of large numbers of gas vacuoles, as sug- 
gested by Klehban. The effect of a large 
number of reagents, spectroscopical analysis 
and the examination of microtome sections, 
all strengthened this theory. As faras could 
be determined the enclosed gas seemed to 
be nitrogen. It would seem that the buoy- 
ancy common to so many Cyanophyceae, 
is particularly due to the presence of these 
vacuoles, for in material of the normal blue- 
green color the plants remained at the bot- 
tom of the dish, while those containing 
vacuoles and consequently of a red-brown 
appearance, always floated upon the surface. 
Improved Methods for obtaining Pure Cultures 
of Fresh-water Algae: Dr. G. T. Moors, 
Dartmouth College. 
The results of some methods for obtain- 
ing pure cultures of algae, by the modifica- 
tion of the nutrient medium, were shown. 
It was found that algae might be separated 
from contaminating forms by a very slight 
modification of the salts upon which 
they are grown. Luxuriant growths of Cy- 
anophyceae were obtained upon a decoction 
of Zamia, with the addition of peptone and 
sngar. It required less than one-half the 
time for algae grown on this medium to 
nearly double the growth of those on min- 
eral salt solutions. The possibility of using 
heat in separating blue-green algae from 
grass-green forms was also referred to. 
A Second Preliminary Report on Plant Dis- 
eases in the United States due to Rhizocto- 
nia : Dr. Benzsamin M. Duecar, Cornell 
University and Mr. F.C. Stewart, New 
York Experiment Station. 
SCIENCE. 
249 
This report presented notes upon the oc- 
currence and destructiveness of American 
forms of Rhizoctonia observed by the authors. 
Since the first report (presented to this So- 
ciety in 1898), the occurrence of Rhizoctonia 
on some entirely new hosts has been ob- 
served, and also upon other hosts new to 
America. As principal host plants among 
vegetables may be mentioned bean, sugar- 
beet, cabbage and cauliflower, carrot, celery, 
cotton, lettuce, potato, radish and rhubarb; 
and among flowers, asparagus, china aster, 
carnation, coreopsis, sweet william and 
violet; also about ten other less important 
hosts. In many cases the Rhizoctonia is 
truly parasitic and undoubtedly the cause 
of the disease in question, as has been abun- 
dantly proved by experiment; but in other 
cases inoculation experiments are yet lack- 
ing. Morphological studies and extensive 
inoculation experiments are in progress to 
determine more carefully the physiology of 
the forms and the limitations of species. 
The Bacterial Diseases of Plants: Dr. ERWIN 
F. Smitu, Department of Agriculture. 
This consisted of a stereopticon lecture 
before a joint meeting of the Society for 
Plant Morphology and Physiology and the 
Society of American Bacteriologists. Three 
diseases were described, namely, the wilt 
of cucurbits due to Bacillus tracheiphilus, the 
brown rot of solanaceous plants due to 
Bacillus solanacearum, and ‘the black rot of 
cruciferous plants due to Pseudomonas cam- 
pestris. Fifty-eightslides made from the au- 
thor’s clear and beautiful photographs and 
photomicrographs were exhibited, showing 
symptoms, location of the bacteria in the 
tissues, etc. Many of these illustrations 
will be published in the near future in Cen- 
tralblatt fir Bakteriologie, 2te Abteilung. 
Notes on the Life History of certain Uredineae : 
M. A. Carteton, Department of Agri- 
culture. (By invitation.) 
