170 NATURAL HISTORY OF THE FARM 
ion made through the bark, from every wound or 
broken twig, the sap flows copiously. It flows first on 
the south side of the tree, where the sun shines, and it 
flows most copiously during the warmer part of the day. 
It ceases at night when the treetop is cooled and the 
pressure equalized. It slackens on cloudy days, and 
ceases altogether when the ground gets warmer. The longer 
the period of alternating bright sunshiny days and sharp 
frosty nights, the greater the amount of sap obtainable. 
The greater, also, is the drain of the food reserve of the 
tree: but the provident maples store more than they need, 
and they are not injured by the loss of such amounts as may 
be obtained by proper tapping. They often have to mect such 
losses through natural causes—such as the tappings of the sap- 
suckers, and the “‘bleeding” from the stubs of broken boughs. 
Other deciduous woody plants lose their sap in similar 
ways. Every vine-grower knows that grape vines, trimmed 
at the time of abundant sap-flow, ‘‘bleed”’ profusely from the 
base of every branch removed—so profusely, indeed, that the 
plant may be weakened by such inopportune treatment. Ash 
and elm and beech and butternut and other deciduous trees 
will yield sap in its season, but only a few of the maples yield 
a sap that is sufficient in quantity, rich enough in sugar, and 
sufficiently well flavored to be important to us. The sugar 
maple is the best maple, both in yield and in quality of 
product: a variety of it known as the black maple, is 
especially esteemed by many growers. Red and silver 
maples yield a copious, but more watery sap. The Oregon 
maple is a western species from which a little sugar is made. 
The yield of the lesser maples and of the related box-elders is 
of no consequence. Most tree-saps, on evaporation, will 
yield some sort of a sweetish treacle; but only the maples 
yield palatable syrups and sugars, whose flavor is improved 
by the non-sugary natural substances present in the sap. 
