282 Frederick Stoivard : 



]*ercentage of acid apparently present in tubers 

 15x0.098x100 ^.^^ 

 ^ "1650 ^ • ^'^' ' 



As we shall shortly see. the distriljiition of the acid al)sorbed 

 is not uniform, hut localised in the buds and the immediately 

 subjacent tissue. 



Again it is ]»robai)ly more correct to state that the evaluation 

 of the percentage of acid- absorbed is too high, for the fall in 

 the titre of the solution is partly accounted for by the adher- 

 ence of the acid to the skin of the treated tuber. 



So far no definite evidence^ has been adduced as to the 

 localisation of the points of entry of the dissolved substances 

 into steeped tubers. 



As we have seen the amounts of sodium chloride and sulphuric 

 acid which diffuse into the steeped tuber are relatively small, and 

 while ordinary quantitive chemical determinations indicate with 

 tolerable precision the general trend of the diffusion processes, 

 these suggest rather than deitinitely establish the fact that 

 absorption of the solute is exclusively confined to the buds. 



The entry of sulphuric acid into the mature blight-free and 

 undamaged tubers, it may be stated, takes place exclusively 

 through the buds. 



The point is capable of precise demonstration : the freshly- 

 cut tuber, Avhether untreated or after steeping in water, on 

 testing with an aqueous solution of methyl orange, gives a 

 distinctly alkaline reaction. It follows, therefore, if, after steep- 

 ing tubers in an aqueous solution of H.JSO4 deeply coloured 

 with methyl orange, for ffve or more hours, and then carefully 

 washing with distilled water to remove the last traces of acid 

 adherent to the surface, a persistent pink colour is demonstrable 

 at any point beneath the skin, that both acid and indicator 

 have been absorbed. If, for example, an intact tuber, the skin 

 of which is undamaged, is thus treated, and sectioned so that 

 the plane of section includes a bud or " eye," it will be found 

 that the bud and the immediately subjacent tissue for the depth 

 of a few millimetres, is more or less distinctly mapped out by 

 a pink coloration, which is intense superficially, and becomes 

 gradually fainter as it is traced internallv. That methyl orange 



