844 Alfred J. Ewavt: 



with the cell-sup. The essential feature of a typical plant cell as 

 compared with an animal cell is that it avoids isosmotic condi- 

 tions, and spends its whole life not quite in distilled water, but in a 

 very dilute solution containing usually not more than one gram of 

 dissolved solids in 1 to 2000 c.c. of water. This water saturates 

 the cell-wall, and the strong solution inside the cell presses the 

 semi-permeable protoplasm against the cell-wall, and stretches the 

 latter until its distension balances the surplus osmotic energy 

 of the cell sap Avhen a condition of the hydrostatic equilibrium is 

 reached. If the cell is now placed in an isosmotic solution of an 

 impermeable salt, the cell wall is no longer stretched, no growth is 

 possible, and the cell is in an entirely abnormal condition. 



Scarlet Nonpareil apples of approximately the same shape and 

 size were selected, only varying a few grams from 800 grams weight. 

 After removing the cuticle from 15 points in areas of as nearly 

 as possible 1 mm. diameter, the apples were weighed and floated in 

 water and 2.5 salt solution for 1 week. The first apple gained 0.6 

 gram per cent, in weight, the second 0.057 grams. In a second 

 experiment the calyx and stalk w^ere covered with paraffin. In 

 distilled water the apple absorbed 0.45 c.c. of water per 100 grams, 

 in the salt solution it lost 0.03 c.c. In 0.5 % and 1.5 % solutions 

 of sodum chloride distinct gains of w'eight were shown, but always 

 less in the 1.5 % as compared with the 0.5 % solution, and in the 

 latter as compared with distilled water, provided that the skin of 

 the apples was without injury or crack so that water could enter 

 only at the prepared points. 



The amount of absorption will depend largely upon whether 

 the osmotic pressure of the j^ulp cells is or is not fully satisfied in 

 the apple before it is immersed in water. Hence it is important to 

 use apples fresh from cool storage, in which the loss by transpira- 

 tion has been slight. In the tests with very dilute poisonous solu- 

 tions, a little of the solution is drawn into the apple at special 

 points where the poisonous action is localised, in addition to the 

 poison reaching the surface by diffusion. In one experiment with 

 1 per 100,000 copper sulphate, 0.4 gram of the solution was 

 absorbed and 2.4 grams of tissue were poisoned, so that to poison 

 1 gram of the pulp cells required at least one millionth of a gram 

 of anhydrous copper sulphate. 



Although prepared apples soaked in 1.5 % and 0.5 % salt solu- 

 tions absorb appreciable quantities of the solution, the prepared 

 spots show at first sight no signs of poisoning and remain colourless 



