APPEARANCES MISTAKEN FOR BITTER PIT. 



27 



it is only when the results of these researches are used to elucidate " The Problem of Bitter Pit " 

 (Part II.) that comment becomes necessary here. In answering the question, Can surface 

 poisoning produce deep-seated Bitter Pit tissue ? he freely acknowledges that " in all the 

 experiments on adult apples the effects were always produced, first at the point where the poison 

 was applied, and thence radiated inwards, but in normal Bitter Pit, the dead tissue may sometimes 

 be deep-seated without any apparent connexion with the exterior." Where the Bitter Pit tissue 

 is entirely deep-seated, and there is no perceptible connexion with the surface, he attributes it to 

 " the absorption of minute traces of poisons through the roots, or less probably, of volatile 

 substances from the air." 



The concluding paragraph of the paper summarizes the salient points as to the relation 

 between Bitter Pit and local poisoning. " On three points, however, it may, I think be stated 

 with confidence, that we are on a solid bed-rock of established fact, namely, that Bitter Pit is, 

 strictly speaking, not a disease at all, but is a symptom of local poisoning, produced in the sensitive 

 pulp cells of the apples, that more than one poison may produce it, and that such poisons may be 

 derived from more than one source." 



When it is affirmed by Professor Ewart that deep-seated Bitter Pit is " the result of the 

 absorption of minute traces of poisons through the roots," there is no notice taken of the action of 

 these poisons on the roots themselves. But, in order to understand this process of absorption by the 

 roots, it will be necessary to glance at the soil solution, and how it gains an entrance inside the plant. 



The supply of water must come from the soil, and from this soil solution the tree draws, 

 through its roots, all the materials required in growth, except the carbon dioxide absorbed through 

 the leaves or other green portions of the plant. The mineral constituents dissolved in this soil 

 solution will vary in amount, and in their degree of concentration. This concentration will affect 

 the growth and development of the lower organisms which are concerned in the fertility of the soil, 

 and if the solution is too concentrated, it interferes with growth. 



It is now believed that there is an optimum degree of concentration at which the plant will 

 grow best. Cultivation prevents excessive concentration of the soil solution, and the effects in 

 this direction of green manuring and fertilizers have yet to be studied. 



But the soil solution, containing the nutritive materials required by the plant, must be 

 absorbed, and the concentration within the cells become more or less equalized with that without, 

 before the plant can be properly nourished. How this is accomplished will now be shown. 



Although the roots are surrounded by the soil solution, the root hairs do not suck in or 

 absorb the mineral constituents dissolved in it like a sponge. They must pass from the outside 

 to the inside of the cells, and there is a membrane or cell-wall lined with living protoplasm, which 

 guards the entrance. This plasmatic membrane, as it is called, only allows certain substances to 

 pass through, by a process of diffusion. When this diffusion takes place through membranes or 

 partitions, it is distinguished as osmosis. 



This diffusion of liquids, that is to say, of substances dissolved in water, was first seriously 

 studied by Graham, beginning in 1849, and it is to him we owe the clear distinction between the 

 colloid or jelly-like and the crystalline states of matter and the introduction of colloid membranes 

 as a means of separating the two kinds of substance. The use of these colloid membranes is of 

 special interest, because the lining membranes of vegetable and animal cells are of this nature. 



In a communication by him to the Royal Society of London, on "Liquid Diflusion applied 

 to Analysis," he thus explains the process : — " A sheet of very thin and well-sized letter-paper, 

 of French manufacture, having no porosity, was first thoroughiv wetted, and then laid upon the' 

 surface of water contained in a small basin of loss diameter than the width of the paper, and the 

 latter depressed in the centre, so as to form a tray or cavity capable of holding a liqu'id. The 

 liquid placed upon the paper was a mixed solution of cane sugar and gum arabic, containing 5 per 

 cent, of each substance. The pure water below and the mixed solution above were, therefore 



