1892. | Briefer Articles. 91 
most frequently elliptical form with the longest diameter 
often from east to west, and if they occur several together on 
the spots in the middle being the largest. He has made a 
series of experiments so as to test the different theories, 
which have been enumerated above. It has been thereby 
proved, that drops of water are unable to cause any kind of 
burning by their own heat. Further, as shown by Sachs, the 
vegetative cell of land-plants is able to stand a heat of 51° C. 
All the experiments, made by the author in that direction, 
gave negative results, so that Neumann’s theory cannot be 
correct. Some experiments were made with water of a 
temperature above 60° C., but even this did not affect the 
As regards the supposition, that drops of water might have 
the same effect as lenses, it is quite clear that drops which 
have fallen on leaves merely represent half-lenses, a fact to 
which already De Candolle has called attention. And it is 
shown by experiments, that only when the drops of water 
were out of contact with the leaves, do they become able to 
Cause a kind of burning, for instance when hanging down 
from the inside of a glass cover. 
The author has come to the conclusion that in most cases 
the burnt spots are due to the poor quality of the covering 
glass, by the air. bubbles of which the sunlight becomes concen- 
trated so as to produce a burning on the leaves.—THEO. 
Hou. 
BRIEFER ARTICLES. 
Cleistogamy in the genus Polygonum.—On page 273, Vol. XVI, 
Borantca GazeTTE, it is noted that “ Mr. Thomas Meehan has found 
cleistogamous flowers in abundance on Polygonum acre and suspects 
the same habit in other species.” On page 314 of the same volume of 
the Gazerre, Mr. T. H. Kearney, Jr., records his observation of 
cleistogamous flowers upon Polygonum acre at Knoxville, Tenn., ac- 
companying his note with figures. Mr. Kearney farther states that he 
has “ searched for cleistogamic flowers on other species of Polygonum 
without success.” 
e me led by the appearance of these notes to state that in my 
‘dies of the genus Polygonum, I have found cleistogamous flowers 
