222 BOTANICAL GAZETTE [ MARCH 
A VERY clear paper by Dr. A. Nabokich, on the functions of aerial roots of 
orchids has appeared in Botanisches Centralblatt 80: 331 ef seg., 1899. He 
shows that the supposed power of their velamen to condense water vapor from 
the atmosphere does not exist, and presents good evidence that these roots 
‘can make use of dew only as it condenses on leaves and stems and reaches 
them in drops. He proves that though they supply the plant with water, 
there is no correlation between transpiration and absorption, where there is 
storage of water. Absorption decreases with the temperature of the water, 
and when the storage factor was eliminated by the saturation of the tissue, 
there was little or no absorption in cold water if transpiration was prevented. 
He recognizes no relation between the presence of leaves with water storage 
and the presence or absence of velamen. The chief function of the velamen, 
he considers to be the protection of the parenchyma from sudden cooling at 
night, especially in the dry season, and in support of this view he lists nearly 
three hundred species showing the relation between the presence of velamen 
and the environment of the species. Those in moist, equable regions show at 
most only a few layers of the velamen, while those living under more variable 
conditions have from a few to eighteen layers. A second function of the 
velamen is the power of adapting the roots to hydrophytic conditions during 
the rainy season, when they are encased in water, and he believes the “white . 
streaks”’ to be air reservoirs to allow them to breathe at this time.—L. 
UNDER THE title “The sexuality of the fungi,” Harold Wager presents % 
a summary of the present knowledge regarding nuclear fusions in the fungi, 
and considers the leading interpretations which have been given to the facts. 
Wager regards it as possible that in Spherotheca and similar forms the devel- 
opment of the ascogonial filament of cells exhausts the energy imparted by 
the preceding fusion of the antheridial and oogonial nuclei; that the energy 
necessary to produce another reproductive cell, the ascus, can only be obtained 
by a further nuclear fusion; and that in the higher Ascomycetes this second 
nuclear fusion has probably replaced altogether the morphologically sexual 
fusion of the simpler forms. This hypothesis may be extended to embraee 
the Ustilaginales and Uredinales, 
It may well be that a deeper insight into sexuality itself and a due con- 
sideration of the later developments in physiology " will lead to views involv- 
ing less of the idea of an energized nucleus.— F. L. STEVENS. 
§ Annals of Botany 13: 575-597. 1899. 
© Logs, JACQUES: Am. Jour. of Phys. 3: 135-138. 1899. 
