1893.] Botany. i 199 
* It is hoped that societies will'send delegates to the Congress. It is 
requested that all persons intending to be present notify the chairman 
of the committee of arrangements at as early a date as possible.” 
The committee, consisting of Messrs Arthur, Bailey, Britton, 
Campbell, Coulter, Coville, Galloway, MacMillan, Robinson and 
Underwood promises to issue a programme of the sessions before the 
meeting. Inthe meantime further information may be obtained of 
the chairman, Dr. J.C. Arthur, Lafayette, Ind.—CHARLES E. Bessey. 
Freshwater Algæ.—Dr. A. C. Stokes has rendered a good ser- 
vice to beginners in the study of the fresh water alge by preparing 
his little book “ Analytical Key to the Genera and Species of the 
Fresh Water Algz and the Desmidiez of the United States.” It con- 
tains 117 pages of matter, and a plate illustrating the genera. As 
brought out by the publisher E. F. Bigelow of Portland, Conn., it is a 
neatly printed, cloth-bound volume, which he sells for the moderate 
price of $1.25. It merits an abundant sale. The following sugges- 
tions taken from the introduction may be useful to beginners: 
“ Algæ and Desmids are singly invisible to the naked eye. It is 
only when they occur in large masses that the eye can take cognizance 
of them. It rarely occurs, however, that the Desmids are so abun- 
dantly congregated that they thus obtrude themselves on the observer. 
When a large quantity has been collected and the vessel placed near 
a window, they will collect in a green film at the surface of the water 
on the lighted side, and there become visible in mass. In the ponds 
and shallows such an occurrence is not common. At times they are 
found so abundantly that by holding a glass vessel of the water up to 
the light they may be seen floating about as minute green objects, 
which the trained eye will recognize and the pocket lens make distinct. 
But these varieties are among the largest of the forms; according to 
my experience they are always exclusively confined to the Closteriums. 
Other large forms, like Micrasterias, at least in the writer’s locality, 
rarely occur in such profusion. To collect the Desmids, therefore, it 
is necessary to collect by faith. The microscopist can know exactly 
what he has only when he gets home and examines the water, drop by 
drop, under the microsco n 
“ With the Alge it is different. These are usually visible to the 
naked eye, as they are almost invariably collected in large masses, 
floating on the surface, submerged just beneath the surface, or attached 
in waving tufts or fringes to sticks and stones and other plants in the 
ponds. The eye of faith is not needed to recognize them. They 
LI 
