Organic Vegetable Gardening

Leaves

The tree obtains nourishment from the soil through the roots, and from the air through the leaves. Both roots and leaves are adapted by nature for the role they play. The leaves of broad- leaved trees consist of the stalk, or petiole, and a thin lamina or blade, which provides the greatest possible surface of contact with the air.

Simple leaves may differ in outline and may be linear - a narrow leaf with parallel sides, at least 12 times as long as it is wide; acicular- a narrow cylindrical leaf with a pointed tip, needle-like in form; lanceolate - basically, a leaf shaped like the head of a lance, with the broadest part below the middle and tapered to a point, but never less than 3 times as long as it is wide; ovate - similar to lanceolate, but always wider, and never more than twice as long as it is wide; egg-shaped; obovate - the reverse of ovate, the stalk rising from the narrow. end; orbicular - a rounded leaf as long as it is wide; cordate - heart-shaped, referring to the lobed base of leaves. rhomboid - diamond-shaped, or roughly so.

Compound leaves are referred as trifoliate if they consist of three leaflets radiating from a single point. If there are five or more of these leaflets and if they radiate from the end of the petiole, the leaf is termed palmately compound.

The rate of transpiration of broad-leaved trees is several times greater than that of conifers. The poplar, aspen, alder, birch and ash have a particularly high rate.

There may be an odd number of leaflets with one located at the tip (terminal leaflet), e.g. the mountain ash, common ash, false acacia (black locust); or an even number of leaflet pairs, e.g. the honey locust and the like.

Only where insufficient rainfall, high temperatures or severe winters and frozen soil prevent the growth of trees do they leave such areas to grass, shrubs and succulents.

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