The Leaves. 83 



packed with fibrous tissue, is much stronger than that 

 of the forest tree. 



125. The Comparative Size of Leaves on a given plant 

 depends much on the water supply during their forma- 

 tion. The^ leaves of sap-sprouts (224), that take an 

 undue proportion of water, are usually very large, and 

 in upright-growing plants, the leaves on the more nearly 

 vertical shoots are usually larger than those on the hori- 

 zontal ones. The more vigorous the plant, the larger, 

 as a rule, are its leaves, and the softer is its woody tissue. 



In plants grown from seed to secure new varieties, 

 large leaves may be taken as evidence of superior root 

 development, which implies capacity to endure drought 

 and, therefore, hardiness. In the apple, the large-leafed 

 varieties are, as a rule, hardier than others, probably 

 because their vigorous roots supply the needed water 

 during the dry season, thus enabling the tree to mature 

 healthy wood and buds which can pass severe winters 

 unharmed (175). 



Crops grown for their leaves, as cabbage, lettuce, to- 

 bacco 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 be- 

 come 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 clogging and die before the stem is fully developed, 

 and in most perennials the leaves endure but a single 



