40 Mr W. Gardiner, On the Physiological [Nov. 12, 



tions of calcic carbonate on such hairs as those of Cheirantkus 

 cheiri as observed by de Bary 1 . 



Finally, until some further and convincing proof is brought 

 forward, it would appear that Sach's statement still prevails, viz. 

 that the exudation of water from the surface of water-glands is 

 dependent upon root-pressure. 



While investigating the physiology of water-glands I was struck 

 with the fact that the exudation of water appeared to take place 

 much more freely in darkness than when exposed to light, and in 

 consequence I instituted a number of experiments to ascertain in 

 how far this was actually the case. These experiments conclusively 

 point to the fact that light retards very considerably the exudation 

 of water, both from water-glands and from those secreting epidermal 

 structures which are not dependent upon, root-pressure, but will, 

 like the hairs of Fuchsia, exude water when cut off from the parent 

 plant. The experiments in question were made upon the following 

 plants. 



1. Water-glands : 



Plants of Saxifraga crustata, Saxifraga spathulata, Vitis 

 antarctica, and Hordeum vidgare. 



2. Secreting epidermal structures : 



Cut-off pieces of Limoniastrum (Statice) monopetalum, 

 Polypodium aureum, and Fuchsia globosa. 



1. Young plants of Hordeum mdgare were grown in a house, 

 the temperature of which was about 73° F. Over some of these 

 plants pieces of newspaper were spread, while certain of them were 

 left uncovered. The former repeatedly exuded large drops of water; 

 while, as regards the latter, the amount was much smaller, and in 

 some instances there appeared to be no exudation at all. 



Potted plants of Saxifraga and Crassida were covered with a 

 bell-jar which fitted to a basin holding water. As long as they 

 were exposed to light, the exudation was scanty, and indeed in 

 some instances not discernible, but after having been put into a 

 dark cupboard — the temperature remaining constant — they exuded 

 large quantities of water, so that the leaves were bathed with the 

 copious exudation. On coming again into light the amount 

 exuded increased but little, and was soon evidently arrested. 



A shoot of Vitis was placed in a manometer and exposed to a 

 moderate mercury pressure, the shoot being under a bell-jar 

 standing on a plate with a perforated bottom. While in the light 

 there was no perceptible exudation, but after having been exposed 

 for some time to darkness, large drops soon appeared on the leaf- 

 teeth. 



1 De Bary, loc. cit. p. 63. 



