The Leaves. 81 
The more vigorous the plant, the larger, as a rule, are its 
leaves. 
In plants grown from seed to secure new varieties, 
large leaves may be taken as evidence of superior root de- 
velopment, which implies capacity to endure drought and, 
therefore, hardiness. In the apple, the large-leafed varie- 
ties are, as a rule, hardier than others, probably because 
their vigorous roots supply the needed water during the dry 
season, enabling the tree to mature healthy wood and buds, 
which can pass severe Winters unharmed (175). 
Crops grown for their leaves, as cabbage, lettuce, tobacco 
etc., are especially liable to be curtailed by drought, and 
hence should be given the culture that best promotes soil 
moisture, as abundant surface tillage and liberal manuring 
(232). 
126. Leaves are Usually Short-Lived because they 
become clogged with those mineral matters taken up with 
the soil water, which are not used by the plant (64), and 
which do not pass off in transpiration (75). In most annual 
plants (337), the older leaves become useless from this clog- 
ging, and die before the stem is fully developed, and in most 
perennials the leaves endure but a single season. In the 
so-called evergreen plants, in which the leaves are usually 
very thick, and are often well protected against evaporation 
by a very strongly developed cuticle (65), the leaves rarely 
live more than a few years. 
127. The Manurial Value of Leaves, that mature on 
the plant, is usually small, since the more valuable fertiliz- 
ing materials they contain pass into the stem before the 
leaves ripen (171). The mineral matters contained in largest 
quantity by leaves are those that are not used by the plant, 
but have been deposited within them in transpiration (126). 
