40 PRACTICAL BOTANY 



and on cooling re-examine : the corky walls, if the 

 reaction be complete, will be found to have lost their 

 definite outline, and to have run together into irregular 

 viscid drops of eerie acid, which is in some measure 

 soluble in the mixture when hot, and is reprecipitated 

 on cooling. 



This reaction may with advantage be performed in 

 the bulk, by cutting some shavings of cork, and boiling 

 them for some minutes in Schulze's macerating fluid : 

 they will be seen to lose shape, and coalesce into a viscid 

 mass : this is soluble in warm alcohol, benzol, &c. 



Stratification and Striation of thickened Cell- walls. 



If the thickened cell-walls of the endosperm of the Date, or of 

 the wood of Pinus, or of the superficial layer of the testa of 

 Linum, be examined under a high power, they will all be seen to 

 show more or less clearly a stratified structure, being composed 

 of successive concentric layers : this may be more clearly seen in 

 various other specimens, a good one being a transverse section of 

 an old branch of Clematis Vitalbaj mount in water, and examine 

 with a high power. 



Observe the thick-walled cells of the pith ; the wall appears 

 to consist of a series of concentric layers; this appearance is 

 described as the stratification of the cell-wall. 



Strip a piece of the bark from the branch, and remove with a 

 needle some of the fibres which compose the internal layer of the 

 bark ; mount in water, tease out with needles, and examine with 

 a high power. 



Observe the dark lines running in the wall of the fibres at an 

 acute angle to the longer axis of them ; note that these lines 

 run in different directions in different layers of the wall of the 

 fibres ; this may be seen by carefully focussing first the superficial, 

 and then the deeper layers of the wall ; these lines are described 

 as constituting the striation of the cell- wall. 



The lines of striation may be very well seen in longitudinal 

 sections of the wood of the Pine. 



