CH. IV] FROST EFFECTS. 97 



the T tube is not quite air-tight it is of no consequence, 

 since the leak affects the leaf and the manometer equally. 

 A good air-tight junction may however be made by 

 Devaux's method^ of melting the leaf stalk into a funnel 

 with gelatine G as shown in fig. 19. 



(121) Frost effects. 



The injection of the intercellular spaces with water 

 can be observed on the frozen leaves of certain evergreens. 

 In a hard frost the leaves of the ivy have a semi-trans- 

 parent, dark green appearance like, but not so dark as, the 

 colour of a water-logged leaf If the leaf is pinched 

 between the finger and thumb the normal light green 

 colour returns to the under surface : the same effect may 

 be produced by dipping a corner of the leaf in lukewarm 

 water. If however the whole leaf including the cut stalk 

 is thawed under water, it does not become light green, 

 but assumes the very dark tiat of an injected leaf In 

 the first case thawing produces injection with air, in the 

 second with water. The explanation given by Moll'' is 

 that the cells of the mesophyll, in freezing, give up water to 

 the intercellular spaces, and that when they are thawed 

 the cells absorb the melted ice in the intercellular spaces, 

 which then fill up with air or water as the case may be. 



(122) Blocking of stomata by water'. 



One arm of a bent glass tube is gently pushed into the 



cavity of an onion leaf and is there firmly secured by a 



ligature of soft cotton or worsted. The other end of 



1 Ami. 8c. Nat. 1889. ^ Archives Nierlandaises, Vol. xv. 



3 Sachs' Physiologic VegStaU, p. 280. 



D. A. 7 



