436 BOTANICAL GAZETTE [November 



If the cut end of a petiole of a leaf of Nymphaea is placed just beneath the water 

 surface while the upper face of the leaf blade is in the air, gas of about the com- 

 position of the air continuously extrudes from the cut end of the petiole with 

 pressures varying from o to 17 cm. of water, and in volumes amounting to 

 several times that of the leaf in course of an hour. Both the pressure and 

 rate of extrusion increase with a rise of the temperature of the leaf and with 

 dryness of the air in contact with the upper surface of the blade, and ceases when 

 the air over the blade is saturated or when the blade is immersed. By piercing 

 the upper surface of the blade of Nymphaea just over the petiole repeatedly 

 with a needle, turning up the margin of the blade, and supporting a little water 

 over the punctures, a great extrusion of air can be demonstrated, increasing 

 with the temperature of the leaf and with dryness of the air over the marginal 

 region of the blade. This is almost identical with the main observations on 

 Nelumbo, and is explained by the same physical principle. Ursprung believes 

 that a considerable part of the gas exchange in leaves of water plants floating 

 or borne above the water is brought about by "hygro-diffusion," but that it 

 plays no considerable role in the gas exchange of land plants with their narrow 

 intercellular systems, and of course no part in submerged leaves. The studies 

 of Ohno and Ursprung now make possible a much more lucid statement of 

 gas movements and pressures in the intercellular systems of plants than was 

 formerly 20 the case. — William Crocker. 



* 



Cytology of rusts.— Investigations of the cytology of Puccinia 

 Falcariae by Dittschlag 21 and of Endophyllum Sempervivi by Hoffmann 22 

 show that the sequence of nuclear phenomena in these forms agrees in its 

 essential details with that of other rusts. Among the facts presented the 

 following are of special interest. In Puccinia Falcariae, which is an autoecious 

 form of the Puccinopsis type, the binucleate phase arises by the lateral fusion 

 of the cells of a palisade-like layer differentiated near the lower middle of the 

 young aecidium. Unlike the mode of origin of binucleate basal cells in 

 the true aecidia of Puccinia Poae as described by Blackman and Fraser, the 

 mode of origin of these cells in Puccinia Falcariae resembles more nearly 

 that usually observed in aecidia of the Caeoma type, in which the fertile cells 

 are not overlaid with a mass of sterile tissue. Occasionally three cells fuse 

 and thus trinucleate basal cells arise. Occasionally the basal cells branch 



form 



trichogyn 



ailed 



cells are not always present, but when they are they occur on both sexual cells. 



20 Pfeffer, W., Plant physiology. Eng. ed. Vol. I. pp. 199- l8 99- 



21 Dittschlag, E., Zur Kenntnis der Kernverhaltnisse von Puccinia Falcariae. 

 Centralbl. Bakt. II. 28:473-492. pis. 3. figs. 6. 1910. . 



"Hoffmann, H., Zur Entwicklungsgeschichte von Endophyllum Sempermvi. 

 Centralbl. Bakt. 32:137-158. pis. 2. figs. 14. 1911. 



