The other method of rejuvenation is to thin out gradually the dead and weakened branches in the old trees and rebuild them gradually, removing only a small portion in any one year. As the new growth is forced out it is used to replace the old wood where possible. Such a system requires more cutting of small branches high up in the tree to be successful, for it must not be opened to sunlight too suddenly or sunburn will result. The cutting of a large number of small branches tends to force the growth of new buds over a large proportion of the tree and if done moderately many of these will quickly develop into fruiting wood. Eventually, many large branches may have to be removed as newer branches are developed, but this must necessarily be a comparatively gradual process. The advantages of this method are that there is no sudden shock to the tree, there is always sufficient leaf surface to care for any extra supply of sap which may be forced into the tree by unfavorable weather and moisture conditions, and cropping will be continuous. [Illustration: Fig. 19.—Same tree as Fig. 18 after pruning. The actual time required to prune this tree was twenty-five minutes. Photo taken February, 1916.] Whatever method of rejuvenation is used, the grower must be very careful from the first to protect all large wounds by some paint or other protective covering, such as asphaltum, to prevent checking and weathering and to keep decay from getting started and working into the heart of the tree. With very large wounds a protective covering must be kept on during the remainder of the life of the tree, or until the wounds heal over completely. INFLUENCE OF CULTURE ON NUTS The effect of culture on the nuts is quite marked. All varieties will vary in size from season to season and in different orchards during the same season, depending on the plant food and moisture supply available during the time the nuts are maturing. Some varieties, notably the Nonpareil, will vary more in size than in plumpness, while other varieties, like the Ne Plus Ultra, are more inclined to produce somewhat shriveled kernels and imperfectly developed shells and the variation in size will not be as great. As the trees bear larger crops the nuts produced are inclined to be smaller. Young, vigorous trees with a light crop will often produce unusually large nuts with comparatively thin shells. The value of a variety, therefore, will depend largely upon its behavior after the trees reach full maturity and bearing. ORCHARD HEATING FOR FROST PREVENTION There has been considerable interest in protecting almonds from frost because of the frequency with which they are subjected to such conditions by reason of their early blossoming habit. The use of orchard heaters in some districts has become a common and successful practice. It is possible to economically control several degrees of frost for three or four nights or possibly more by a judicious use of heaters.