igoo-i.] Effects of Water on Foliage Leaves. 345 



are generally resorbed by the plant. Carbonates as incrustations may 

 serve to store up, in the presence of moisture, COo at night, and utilize 

 the same as the bicarbonate is reduced to the carbonate in the day time. 

 Incrustations may be, therefore, not only an adaptation to retain water 

 in desert countries, but also to utilize to the full the loss of CO2 caused 

 by respiration. CaCOs, though insoluble in water, may be absorbed if 

 water and CO,, be present. 



Distilled water becomes alkaline, generally, if allowed to remain 



upon leaves of plants for a shorter or longer period of time. 



* 



Certain plants adapted to a moist climate may be made to take in 

 all the food necessary for growth through the leaves. Distilled water 

 used as a spray acts for a time as a stimulus to growth. It may be that 

 it acts as a means of drawing from the plant surplus alkaline salts 

 which, if formed in too large quantity in the cells, might become harmful. 

 Calcium and sodium compounds, and also potassium oxalate have been 

 extracted from leaves by distilled water. Rain water may act as a 

 stimulus in this way. 



Solutions if applied to the surfaces of detached leaves, or to leaves 

 upon the plant are generally absorbed as shown by the increased content 

 of ash. Solutions, so applied, often stimulate a certain portion of the 

 tissue to an abnormal development. The ring produced upon a leaf by 

 the application of a drop of solution, is the result of the peculiar action 

 of the evaporating drop. 



Solutions applied to the cut ends of the petioles of leaves are 

 generally conveyed to the minute terminations of the tracheids, where 

 they kill the tissue in one of two ways: — (i) by drawing water 

 osmotically from the cells into the intercellular spaces, producing a 

 translucent appearance of the tissue ; (2) by chemical action, — upon the 

 walls of the cells, (b) upon the protoplasmic membrane, (c) upon the 

 protoplasm as a whole. The first determinable reaction after death is 

 alkaline, even though the tissue be killed by an acid. Some leaves will 

 remain green and fresh longer in a dilute solution of the poison lead 

 acetate, than they will in either distilled or tap water. This applies 

 to leaves which ordinarily wilt away in water in a fortnight or so. 



Certain substances in solution ascend through the blade of a leaf, at 

 rates which vary as the lengths of the different veins of this leaf, and the 

 area of the part affected is symmetrical to the area of the whole leaf. 



The lithium test gives rise to error because the water ascends faster 



