Researches in Vegetable Physiology. 151 



plant of Elodea canadensis which had received the rays of the 

 sun for three hours, continued to produce currents of gaseous 

 bubbles in diffused light, and did not stop until nine hours 

 afterwards, when the night had already long come on. In 

 another experiment, an insolation of one hour produced gaseous 

 currents which were continued for three entire hours in com- 

 plete darkness. According to these observations, therefore, 

 the vegetable tissues are in a manner endowed with the pro- 

 perty of storing up the solar light. Such a phenomenon as 

 this may enter into the group of those which are designated 

 under the name of phosphorescence. 



M. Barthdlemy* has investigated the function of the cuticle 

 (that uniform layer which in general clothes the epidermis of 

 plants) in accordance with the principles of Graham with re- 

 gard to colloids. He has arrived at the conclusion that, in the 

 exchanges of gaseous molecules between the plant and the 

 atmosphere, the oxygen and carbonic acid pass especially 

 through the cuticle (upper surface of the leaves), whilst the 

 nitrogen makes a way for itself through the stomata (lower 

 surface). 



To the phenomena which the action of the luminous rays 

 give rise to in the plant, those which originate in the absence of 

 these same rays are most naturally related. It is by this title 

 that a curious work by M. Kraussf on the causes of the de- 

 formation of etiolated plants figures here. These changes are 

 well known, and present themselves under two apparently very 

 different forms ; certain organs, and especially the limbs of the 

 leaves, when in the dark, undergo a complete arrest of deve- 

 lopment, and are far from acquiring their normal dimensions ; 

 others (for example, the internodes of the stems) become, on 

 the contrary, much more elongated than usual, and attain di- 

 mensions several times exceeding their normal size. 



These apparently irreconcilable anomalies depend upon 

 entirely different properties of the tissues. 



The etiolated leaves are arrested at the point at which, 

 under normal conditions, they would have begun to receive 

 the luminous rays — that is to say, at their issue from the scales 

 of the bud. From this moment a normal leaf is called upon 

 to suffice for itself ; starch soon makes its appearance in the 

 cells whose position brings them first into relation with the 

 luminous rays — that is to say, in those of the teeth, nervures, 

 &c. It is upon this starch that all the subsequent growth of 

 the leaf depends ; that which is enclosed in the interior of the 



* Ann. des Sci. Nat. 5e ser. tome ix. p. 287. 

 t Priugsheim's Jahrb. vii. p. 209. 



