28 



BITTER PIT INVESTIGATION. 



separated only by the thickness of the wet sized paper. After 24 hours the upper liquid appeared 

 to have increased sensibly in volume, through the agency of osmose. The water below was found 

 now to contain three-fourths of the whole sugar, in a condition so pure as to crystallize when the 

 liquid was evaporated on a water bath." 



Here we see that the sized paper does not act as a filter to allow the substances contained 

 in the water to pass indiscriminately through, but diffusion takes place through the water contained 

 in interspaces in the colloid substance. In this case the sugar only passed through, and " the 

 membrane is always permeable for a certain substance, when this substance is soluble in the 

 material of the membrane." That this is so was afterwards clearly demonstrated by Nernst. It 

 is known that ether is soluble in water as well as in benzene, but that benzene is soluble in ether 

 only, and insoluble in water. When a quantity of benzene and a quantity of ether are separated 

 from each other by a layer of water, a continuous stream of ether passes through the water, but 

 there is no streaming of benzene in the opposite direction. Nernst carried out the experiment 

 by substituting an animal membrane saturated with water for the layer of liquid water. A glass 

 funnel was connected with a glass tube, and the benzene was poured into the funnel, which was 

 closed with the saturated membrane. The funnel was then dipped into a vessel containing ether, 

 and, after a csrtiin time, the liquid rising in the glass tube showed the streaming in of the ether. 

 The ether, soluble in water, passes through the membrane, while benzene does not, and an osmotic 

 pressure or resistance is produced on the side of the benzene. The membrane does not act like 

 a sieve, and Czapek, in his " Chemical Phenomena in Life," says, " All signs show rather that 

 solution affinities play the most important part in diosmosis." 



It has also been shown recently, by Professor Adrian Brown, that cereal grains, such as 

 barley, are provided with a lining membrane, close to the outer skin of the seed, which acts as a 

 differential partition, so that the food materials stored up in the seeds should not pass outwards 

 during germination, nor harmful materials pass in to check or stop growth. 



Although, as Professor Armstrong points out, in an article in Science Progress for April, 

 1912, " We have consequently to consider the diffusion not of a single substance, but of an 

 unknown number of substances, and the problem becomes one of great complexity," yet it is clear 

 that the assumption of Professor Ewart, that poisonous substances are absorbed by the roots, and 

 injure the fruit, is not proved. Such substances, if admitted, would certainly have an injurious 

 influence on the roots themselves, as well as on the whole tree. Yet it is the young and vigorous 

 trees which pit badly, and the trees are otherwise quite healthy which are subject to it, and even 

 the roots of the Prince Bismarck tree (Fig. 133), which had been sprayed with arsenate of lead, so 

 far showed no ill effects. 



It seems to me that if the theory of local poisoning is to be proved or disproved, 

 investigation should begin at the roots, and not at the fruits. The remarkable sensitivity of the 

 pulp cells of the apple to poisons has been shown. What about the sensitivity of the delicate 

 cells of the root ? 



Professor Ewart seems to have confined his attention exclusively to the pulp cells, without 

 taking into account the fact of prime importance in connexion with Bitter Pit, that these cells are 

 permeated by a rich supply of vessels which convey the food materials to them, and on which their 

 very existence depends, and I venture to think that if these vessels, as well as the wonderful vascular 

 network immediately beneath the skin, where the Bitter Pit originates (see Figs. 83, 86, 90), had 

 been recognised, he would have arrived at a very different conclusion. 



^ I cannot better conclude this section than by quoting the remarks of Professor P. J. O'Gara 

 (68), in his article on the " Absorption of Arsenic by Apples from Spray," where he shows how totally 

 different the peculiar spotting of apples caused by arsenate of lead is from Bitter Pit. " A careful 

 examination of the spotted apples shows that only the epidermal and sub-epidermal cells are 

 injured, so that the injury may be said to be only skin deep." 



