28 MANUAL OF FRUIT DISEASES 
the flesh in all directions. These sap-tubes are the channels 
through which water and mineral food from the soil are carried 
to the living cells of the fruit. The apple is enclosed in a 
smooth, water-proof skin made up of a layer of cells, the outer 
walls of which are thick with a waxy infiltration of a water- 
proof nature. Scattered here and there, but most abundant 
toward the blossom-end of the apple, are minute openings 
through the skin known as lenticels. They are visible to the 
naked eye on certain varieties as minute brown specks. 
Through these lenticels air passes into and out of the apple; 
and water brought from the roots passes out as vapor. This 
process of water elimination is known as transpiration. Great 
quantities of water pass out in this way if conditions are favor- 
able. Low humidity, high temperature, rapid movement of 
the wind, and intense light facilitate the process. If plenty of 
water is supplied by the roots, the process of transpiration re- 
moves the great bulk of it as vapor through the lenticels. If 
the supply of water is deficient, but at the same time conditions 
favor transpiration, then too much water is removed and 
wilting results. 
When the brown spots are examined with a compound micro- 
scope it is found that the affected cells are collapsed or perhaps 
broken, and hence the tissue sinks, forming a pit. Whether the 
cells are merely collapsed or are broken is a question yet unde- 
cided. The cell contents are lacking for the most part, only © 
starch grains, which were not converted into sugar during the 
ripening process, remain. Their presence is regarded as proof 
that the injury to the cells occurred before the ripening of the 
fruit. The cells are brown and have every evidence of being 
dead. Their brown color and their lack of sap, and therefore 
their dry texture, give the described appearance to the whole 
diseased area. Careful search will show that the brown spots 
always arise in close connection with a branch of the sap-tube 
system. : 
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