536 Report of the Progress of Vegetable Physiology in 18S6. 



very much ; if in the earth, the roots generally first die off', 

 and then sometimes little air-roots become developed on the 

 stem. This pha?nomenon seems to be very common when the 

 roots are in a suffering state, or if they cannot properly develop 

 themselves: thus Jablonski(/.c. p. 21 1 ) saw the stem of a cabbage 

 plant which grew in a very imperfect state in purified flowers 

 of sulphur, send forth several similar air-roots ; and I have 

 noticed it in balsams and in maize, &c. when the roots had 

 been destroyed in the earth by insects. 



Dutrochet* has again published several observations on the 

 respiration of plants, which are of very high interest ; it is, 

 however, not every physiologist that might be inclined to agree 

 with the conclusions which Dutrochet has deduced from his 

 experiments. We will first give a general notice of the ob- 

 servations from which Dutrochet set out ; for he is of opinion 

 that the glands of the epidermis, as Amici is said to have de- 

 monstrated, tend to close their stomata as soon as they are 

 brought into contact with water. However, I have not been 

 able to confirm this alleged observation, and hence some 

 doubts may be had respecting the conclusions founded on it. 

 Dutrochet had previously published an observation to show 

 that the air in the air-receptacles of Nymphcea lutea were 

 richer in oxygen the nearer they were to the leaves ; whence 

 might be inferred that the oxygen was impelled from the 

 leaves through all the respiratory organs. On the other hand, 

 I will mention an observation which contradicts this ; for if 

 on a hot day we place a hardy specimen of Calla cethiopica 

 partly under water, and cut some of the petioles of the leaf off 

 just above the surface, we are able to observe that from the 

 influence of the solar light, a great quantity of air continually 

 flows from the divided air-receptacles ; but this air appears 

 also to be exceedingly abundant in oxygen, for ignited char- 

 coal shines much the brighter in it. 



Dutrochet placed a severed leaf of a NympJuza under water 

 and observed how it disengaged oxygen, by the action of solar 

 light, only from the divided apertures of the air-ducts of the 

 petiole; he remarked the same circumstance in severed leaves 

 of Hydrocharis Morsus rance^ Potamogeton sericeum and My- 

 riophyllum spicatum. This latter plant lives entirely under 

 water, and possesses no stomata. But if we allow the leaves 

 of Nymphcea and Hydrocharis to float as in their natural state 

 on the surface of the water, the expiration of oxygen ceases 

 at the sected air-ducts of the stem. Does this disengagement 

 of gas cease if the ends of the divided leaf-stalk are bent up- 

 wards? If on the contrary severed leaves ot'Nym])hcea were 



• Rechervhes sur la Respiration dcs Vegetaux. — Institut, 1836, p. 358. 



