1911] CURRENT LITERATURE 157 
themselves. In agreement with Brown and Escompg, he states that loss of 
water vapor from leaves is through static diffusion, and that it is proportional 
to the differences of density of the vapor inside and outside the leaf. RENNER 
urges, as a thing of great importance, that the rate of diffusion will be inversely 
modified by an increase in the distance between the region of minimum density 
outside the leaf and the maximum density within the leaf. It is with methods 
by which this distance is modified that he is mainly interested. If the distance 
is great, the gradient is low and the flow is slow; if the distance is small, the 
gradient is high and the flow fast. One way in which this distance is increased 
in still air is by the water vapor cap which forms over the surface of the leaf. 
The larger the leaf, the greater the average thickness of the vapor cap. For 
this reason, in still air the amount of transpiration does not vary with the sur- 
face of the mature leaves, but is proportionally less for the larger leaves. 
RENNER believes that if the air were absolutely still it would vary as the diam- 
eter of the leaves. 
Winds increase the transpiration of small mature leaves by a much greater 
percentage than it does the large ones. In wind the transpiration is propor- 
tional to the surface of the leaves. Again, the distance between the internal 
maximum vapor pressure and the external minimum may be increased by ex- 
ternal or by substomatal cuticular cavities; if of the same size and shape, 
RENNER finds that the two have equal effects. 
RENNER devised a means of experimentation by which he located the point 
of saturation within a rapidly transpiring leaf. He believes it often lies some 
distance from the stomata. In such cases a considerable system of intercel- 
lular spaces is involved in the diffusion. He emphasizes the fact that in 
such cases the stomata, if open, are only a small part of the diffusion canals, 
and therefore play a small part in the control of transpiration. In a similar 
way their importance as controlling factors is modified by internal and external 
cuticular chambers, and even by the vapor cap.—WILLIAM CROCKER. 
Infection experiments with rusts.—In a preliminary report of some infec- 
tion experiments made near Neuenburg (Switzerland), MiHteNTHALER* 
shows that teleutospores of the coronata type of Puccinia from Calamagrostis 
varia produced aecidia on Rhamnus alpina and R. Purshiana. Aecidiospore 
from these reinfected Calamagrostis varia and C. tenella among several grasses 
tried. Aecidiospores collected on R. cathartica produced uredospores on 
Bromus erectus var. condensatus, Festuca alpina, F. arundinacea, F. gigantea, 
and F. varia. The uredospores thus produced on Bromus erectus var. conden- 
satus could be transferred to B. erectus and its var. condensatus, B. inermis, 
B. sterilis, and B. tectorum. 
In continuation of his cultural work on the Uredineae, ARTHUR'S reports 
4 Mt Sore gu: F., Infektionsversuche mit Kronenrosten. Centralbl. Bakt. 
Il. 26:58. 1 
eae J. C., Cultures of the Uredineae in 1909. Mycologia 2:213-240. 
IgIo. 
