of a tree like the oak his calculations have to be well made beforehand, for the tree may have to stand for from 120 to 200 years before it is cut. Left alone it may live for 1,000 years, but the proportion of good timber in trees after a certain age rapidly diminishes—a fact that has also to be reckoned with.
It is quite different, however, when trees are required for seed purposes. The oak hardly bears fruit at all before it is fifty to sixty years old, and seventy to eighty years is a better age for the purpose; but, as with other trees, to produce really good seed the oaks must be isolated, or nearly so, so that they get the maximum of light and air. Consequently a modification of procedure has to be made when seed-trees are required.
When the fruiting period has once been reached the tree goes on producing acorns every year; but it is noticed that heavy crops of good seeds only recur every five (or perhaps three) years or so, the yield in the intervals being inconsiderable. This is in accordance with Hartig's discovery that in the beech, for instance, the tree goes on storing up nitrogenous materials and salts of phosphorus and potassium during the first seventy or eighty years of its life, and then suddenly yields these stores to the seeds; the drain is so exhausting that it requires three to five years to re-store sufficient of these substances for another "seed-year." The season or weather is also concerned in the matter.
Of course there are very many other details to be