Observations on Stomata. 415 



ably prolonged opening of the stomata a phenomenon which requires 

 further investigation. 



Baranetzky* showed that slight degrees of disturbance affect 

 transpiration. The hygroscope gives no evidence of increased tran- 

 spiration when the disturbance is slight. When the plant is violently 

 shaken the leaves become flaccid and the stomata " close," and in 

 some cases the closure is preceded by increased transpiration, 110 

 doubt due to temporary opening of the stomata, induced by the 

 guard cells being released from epidermal pressure before they have 

 lost their own turgor. 



N. J. C. Miillerf showed that stomata may be closed by electric 

 stimulation ; my experiments show that while a strong shock narrows 

 the stomata, a weaker one opens them, no doubt owing to the tem- 

 porary loss of epidermal pressure. 



Some experiments on poisonous gases and vapours were made. 

 Chloroform and ether slowly " close " the stomata, which finally 

 reopen in a normal atmosphere. Pure C0 2 also slowly closes the 

 stomata. 



The hygroscope is well fitted to demonstrate the fundamental facts 

 in relation to light. The fact that the storaata are widely open in 

 sunshine is well known ; the difference between bright and less 

 bright diffused light is not so well known, nor the fact that in 

 dark stormy weather the stomata may be nearly closed by day, even 

 in summer. The effect of difference of illumination is well shown 

 in certain leaves having stomata in both surfaces, e.g., Iris, Narcissus, 

 and the phyllodes of Acacia cyclopis. In these the stomata on the 

 illuminated surfaces are much wider open than on the less brightly 

 illuminated sides ; and when the plant is reversed in position in 

 regard to light, the stomata rapidly accommodate themselves to the 

 change in illumination. 



The most interesting fact in regard to the effect of artificial 

 darkness is that it is more effectual in producing closure in the after- 

 noon than in the morning ; and, conversely, illumination opens 

 closed stomata more readily in the morning than later in the day. 

 These, together with other observations, tend to show a certain 

 amount of inherent periodicity in the nocturnal closure of the 

 stomata. Another fact of interest is that in darkness prolonged for 

 several days the stomata gradually open. This last observation is 

 used in the section on the mechanism of the stoma as an argument 

 against the prevalent view that the stoma closes in darkness, because 

 in the abeyance of assimilation the osmotic material, on which the 

 turgor of the guard cells depends, ceases to be manufactured. 



* c Bot. Zeitung,' 1872. 



+ Pringsheim's ' Jahrbiicher,' vol. 8, 1872. 



