




1901 | CURRENT LITERATURE 211 
and scientific value. Some such careful study of a large number of floral 
areas is an absolute necessity to a correct understanding of the complex 
climatic and ecologic factors governing the distribution of trees. Indeed, in 
the last atlas" issued by the department an approach has been made to such 
a realization. This atlas contains a brief summary of the vegetal and cli- 
matic features, a map of the floral features, and three maps showing precipi- 
tation, evaporation, and types of rainfall—H. N. WHITFOR 
THE STUDIES of Brenner™ on succulent plants must prove of great inter- 
est to all physiologists and ecologists. His work was experimental and for 
the most part on the Crassulaceae and Mesembryanthemum. After a dis- 
cussion of the normal anatomy, he describes the effects produced on succu- 
lent plants by moist air. The most striking effect in Sedum is pronounced 
internodal elongation, which the author refers to the increased turgor inci- 
dent to lessened transpiration. At first the leaves are fleshy, but later leaves 
are larger and thinner and placed like normal fleshy leaves in dry air in the 
form of a rosette. There is thus a striking correlation between stem elonga- 
tion and leaf form. Another effect of moist air on the leaves is epinasty, so 
that the new leaves place themselves at right angles to the stem; when these 
plants are placed in a dry chamber hyponasty is shown. Notable changes in 
anatomy are also induced. In two plants the normally straight side walls o 
the epidermis become wavy, and doubtless give greater mechanical strength 
to the otherwise weakened leaf. The tangential increase of the epidermal 
cells as against the radial is very noticeable, though Brenner is at a loss to 
find a physical explanation therefor. The stomata at first are the same in 
number as on normal leaves, though of course they are farther apart, since 
the leaf is larger. On later leaves the stomata are more numerous though 
the number per unit area may be much as in normal leaves. There is a 
decrease of the storage tissue and an increase of the chlorophyll tissue, 
though the cells in the latter tissue are more nearly isodiametric than i in dry 
air. The vascular system and air spaces are decreased in moist air; the 
reduction in the bundles is rather in number of cells and pi rise thas 
in cell size. The author finds the dry weight and ash and also the acid con- 
tent to be less than in normal plants. At first moist air increases the size of 
the chloroplasts, though they decrease in size later, pointing to an apparent 
readjustment to the new conditions. 
Various comparative physiological experiments were made on plants 
grown in dry and moist air. In Mesembryanthemum nutation movements 
were noticed in the latter but not in the former. Normal leaves in normal 
air transpire the same per unit area as do moist-air leaves in moist air, 
though the leaf form is very different. This observation is very instructive 
* HILL, ROBERT T.: Topographic atlas of the Texas region, pp. 12. p/s. 77. 1900. 
5 Flora 87 : 387-439. 1900. 
