72 The Plant World. 



ducing a book which will be indispensable to any one who is 

 desirous of an acquaintanceship with fossil floras, and it is need- 

 less to add that in mechanical workmanship the book is every- 

 thing that the imprint of the Cambridge University Press im- 

 plies. — Edward W. Berry. 



Air in Plants. — A recent article by N. Ohno * calls atten- 

 tion to a phenomenon of gas difi"usion and the results thereof 

 which may be of considerable importance in plant physiology. 

 He observed that the leaves of the lotus {Nehcmbo nucifera) con- 

 tinually give off air bubbles from their middle portion during 

 bright sunlight. He proved that the gas is really atmospheric 

 air and that its exudation has no connection with photosynthesis. 

 Conditions which promote evaporation cause an increase in the 

 rate of appearance of these bubbles, which are best seen by 

 placing drops of water on the leaf or by partially filling the cup- 

 shaped receptacle formed by the middle portion. Ohno was 

 also able to measure the gas pressure which forces these bubbles 

 out of the leaf, and found it to rise, under the most favorable 

 conditions, to a magnitude greater than that represented by 

 forty millimeters of a mercury column. 



The explanation of the phenomenon appears to rest on that 

 of the observation of Dufour and others, described and explained 

 by Kundt, and referred to in Pfeffer's Physiology, Vol. I, p. 204. 

 The observation and its explanation run as follows. If a porous 

 clay vessel, otherwise closed, be attached to a tube which dips 

 slightly below a free water surface, and if the porous clay be wet 

 with water, alcohol, or some other volatile liquid, air bubbles are 

 seen emerging from the end of the tube and rising in the water. 

 The phenomenon continues long after an amount of air equal to 

 the volume of the vessel has exuded, which shows that this air 

 is in nowise related to the original air in the vessel. A quick 

 way to demonstrate the action is to use alcohol and ignite it on 

 the porous clay. In a few minutes a hundred or two cubic centi- 

 meters of air may be collected from a vessel containing no more 

 than fifty cc. To explain the action we consider that the gas 

 pressure outside of the clay chamber is due to a large partial 

 pressure of air and a much smaller one of water vapor, the 

 amount of the latter depending upon the humidity of the air. 



*Ohno, N., Ueber lebhafte Gasausscheidung aus den Blaitem von Nelumbo nucifeia 

 Gaertn. Zeitschr. f. Botanik, 2, heft 10, 641-664, 1910. 



