338 HOW CROPS GROW. 
monia-salts gathered by the roots, is united to carbon, hy- 
drogen, and oxygen, in the formation of albuminoids. 
Besides sugar, malic acid and minute quantities of al- 
bumin exist in maple sap. Towards the close of the 
sugar-season the sap appears to contain other organic sub- 
stances which render the sugar impure, brown in color, 
and of different flavor. 
It is a matter of observation that maple-sugar is whiter, 
\purer, and “grains” or crystallizes more readily in those 
years when spring-rains or thaws are least frequent. This 
fact would appear to indicate that the brown organic 
matters which water extracts from leafmould may enter 
the roots of the trees, as is the belief of practical men. 
The spring-sap of many other deciduous trees of tem- 
perate climates contains sugar, but while it is cane sugar 
in the maple, in other trees it consists mostly or entirely 
of grape sugar. 
Sugar is the chief organic ingredient in the juice of the 
sugar cane, Indian corn, beet, carrot, turnip, and parsnip. 
The sap that flows from the vine and from many culti- 
vated herbaceous plants contains little or no sugar; in 
that of the vine, gum or dextrin is found in its stead. 
What has already been stated makes evident that we 
cannot infer the quantity of sap zm a plant from what may 
run out of an incision, for the sap that thus issues is for 
the most part water forced up from the soil. It is equally 
plain that the sap, thus collected, has not the normal 
composition of the juices of the plant; it must be-diluted, 
and must be the more diluted the longer and the more rap- 
idly it flows. 
Ulbricht has made partial analyses of the sap obtained 
from the stumps of potato, tobacco and sun-flower plants. 
He found that successive portions, collected separately, 
exhibited a decreasing concentration. In sunflower sap, 
gathered in five successive portions, the liter contained 
the following quantities (grams) of solid matter ; 
