186 XIV. CORK LENTICELS. 



staining arises from the presence of fatty bodies in the corky 

 and cuticularised membranes. The corky walls and the cuticle 

 agree with oils in so far as to be stained after prolonged action 

 (several hours or more) with a solution of alkanet in 50 per ce"nt. 

 alcohol, albeit not so strongly. Both these reactions enable 

 us to distinguish between corky or cuticularised and lignified 

 membranes, the ordinary relations of which with stains are much 

 alike. If a section is stained in magenta (fuchsin), dissolved in 

 50 per cent, alcohol, and then washed in absolute alcohol, after a 

 short while the colour is left only in corky and lignified mem- 

 branes ; with longer washing it is left in the cutinised membranes 

 only. 



With chlorzinc iodine the cork cells colour yellow to yellow- 

 brown, the younger darker than the older, their tertiary layers 

 the darkest. With potash the cork cells become yellow, boiled 

 in concentrated potash balls and granular masses of a yellow 

 colour are formed. With the maceration mixture (chlorate of 

 potash and nitric acid) we obtain a reaction for Ceric acid. If 

 un warmed, the mixture first acts by colouring the cork cells 

 yellow-brown, besides which all their parts become clearer. If 

 the preparation is now boiled upon the object- slide, more of the 

 reagent being added if necessary, in a little while only the corky 

 layers of membrane remain ; these finally swell and fuse into 

 a colourless, oil-like globular mass. This is the so-called eerie 

 acid, which is readily soluble in boiling alcohol, and still more so in 

 ether, but is insoluble in sulphuric acid. If pretty concentrated 

 solution of chromic acid is permitted to work upon a section, of 

 this there finally remains, as before, only the corky layers of 

 the cork cells. After a longer time these themselves become so 

 transparent that it is difficult to find them again, although they 

 do not disappear. Notwithstanding that the middle-lamellae 

 have been dissolved, the secondary thickening layers adhere to 

 one another. 



The most recent researches show that though the suberin of 

 corky walls, and the cutin of cuticle and cuticularised walls, very 

 closely resemble one another, they are not exactly the same. 

 Phellonic acid, which is always present in cork, is not so in 

 cuticle. Cutin resists potash more strongly than does suberin. 

 After heating to 300 C. in glycerine, corky membranes generally 

 leave behind a product of decomposition which is easily soluble 

 in chromic acid ; cutin does not. 



