3 
; 
3 
. 
1898 | CURRENT LITERATURE 69 
position just preceding Musci, but between the Musci and pteridophytes. 
He believes that the group is more nearly allied to the pteridophytes than to 
the Hepatice. 
An artificial key to the Hepaticae, Musci, and Anthoceroteze is given, 
based entirely upon archegonium characters. This recalls Treub’s effort to 
base a classification upon chalazogamy. 
No mention is made of Campbell's recent book upon mosses and ferns, 
although quite an extensive bibliography is given. A perusal of this book 
would probably have added to the value of M. Gayet’s monograph.—C. J. C. 
WIESNER has made another valuable addition to his various studies on 
the influence of rain on the plant world. Readers of the GAZETTE will 
remember in this connection his studies on ombrophilous and ombrophobous 
organs. His latest work has been to observe the mechanical influence of 
rain on plants.*3 After referring to the researches of Jungner and Stahl on 
the adaptations of tropical leaves to rain, the author refers to the common 
view among botanists that rain works mechanical injuries on plants, although 
this view is based wholly on theory rather than on actual experimentation. 
Wiesner found that the heaviest rain drops, whether in or out of the 
tropics, weigh but 0.168", and that the greatest velocity attained is but 7™ per 
second. Hence the “greatest living force”’ possible is but 0.0004**™. Rarely 
more than six heavy drops fall per second on a space of 100**. Water 
poured from a watering can so slowly as to strike the ground in drops has 
from fifty to one hundred times this force. The author then records experi- 
ments on leaves and flowers and finds, for example, that the corolla of 
Impatiens noli-tangere, when placed on a firm support, is injured by a sphere 
of lead weighing one gram falling 4°" (=0.000004*"); while swinging free 
in nature it requires a force of 0.08**™ to produce an injury, 7. ¢., a force 
20,000 times as great, and a force 200 times as great as that exerted by the 
severest rain! Similar results are obtained from all experiments, so that the 
author concludes that leaves and flowers are practically never mechanically 
injured by rain alone where swinging free in nature. This conclusion might 
be reached a priori from the fact that tropical leaves, which are exposed to 
more rain than plants of our latitude, are nevertheless less adapted to 
Stand mechanical injury; for example, they absorb water more freely, thus 
becoming less protected from mechanical impact, and even when dry they 
“re more readily perforated than our ordinary leaves. 
Vhile rain produces little or no mechanical injury when unaccompanied 
by wind, the destruction due to wind and rain combined is quite patent, but 
although the water may here do actual mechanical harm, the wind rather 
* Bor. Gaz. 20: 112. 189 
- Untersuchungen iiber die mechanische Wirkung des Regens auf die Pflanze. 
Ann. Jard. Bot. Buit. 1g: 277-353. 1807. 
