750 RECORD OF CUKRENT RESEARCHES RELATING TO 



weiglit of dry organic matter was tlie same in the green and in the 

 etiolated phxnts. The plants which had grown in the light, but in 

 air free from carbonic acid, and where assimilation could not take 

 I^lace, did not bear the slightest resemblance iu form to etiolated 

 plants. They were of perfectly normal habit. 



Effects of Submersion on Aerial Leaves, and of Water on 

 Floating Leaves.* — Previous experiments by E, Mer on the ivy, 

 haricot, and Tropaeolum, had led to the following conclusions, viz. : — 



1. Throughout the whole submersion the leaves have no power of 

 producing starch, and they rapidly lose that which they contained. 



2. Their development is greatly retarded, and they never acquire 

 their normal dimensions. 



3. They die more or less rapidly, according to the sj)ecies. This 

 is generally preceded by the infiltration of the lamina. 



Further investigations by the same authority show that the cause 

 of the death of submerged leaves is not so much asphyxia as starva- 

 tion, from the failure of the power to assimilate consequent on the 

 diminished supply of oxygen. The perishing is also greatly 

 accelerated by the infiltration of the tissues, which, however, does not 

 usually take place until the starch has completely disappeared. 

 Leaves of plants with bulbous roots suffer much less than others by 

 immersion, because of the constant supply of assimilated food- 

 material from the reservoirs. The infiltration is perceptible chiefly in 

 the intercellular spaces, but, in order to reach these, water has first to 

 penetrate the epidermis. 



In the case of aquatic plants with floating leaves, M. Mer shows 

 that these leaves are also killed, like aerial leaves, by submersion, 

 and that the starch which they contain is produced entirely on the 

 up]3er surface, and not from the carbonic acid dissolved in the water. 



Absorption of Water by the Lamina of Leaves.! — The following 

 results have been arrived at by E. Mer, in continuation of his 

 researches on the eflects of submersion on the leaves of plants : — 



1. The lamina of leaves can absorb water, both when they are 

 entirely submerged after having lost their turgidity, and when placed 

 in contact with the liquid only by a portion of their surface, the other 

 part remaining exjiosed to transpiration. 



2. Absorjition is more active by the lower than the upper surface, 

 and more so in those leaves which have a thin than in those with a 

 thick cuticle. In the former it is sufiicient to suspend desiccation in 

 the interuodes and the remaining leaves which are not submerged, 

 when these organs do not receive water from any other source ; it is, 

 however, not sufficient to preserve the turgidity of the roots. In the 

 latter the absorption of water is not sufiicient to recover the weight 

 which they possessed before fading. 



3. The absorption is not merely local, since it restores turgidity 

 in the neighbouring organs. All the tissues of a plant are more or 

 less capable of absorbing water. This can be proved in a variety of 

 cases. 



* 'Bull. Soc. Bot. France,' xsv. (1878) pp. 79 and 89. 

 t Ibid., p. 105. 



