The possibilities in this field will be much expanded with increasing knowledge on the specific requirements of various tree species for good root growth.
As is described in detail in the last part of this article, practical conclusions could be drawn from better knowledge about root growth.
In spite of this, relatively little is known about growth behavior of roots.
Water uptake and mineral absorption, according to modern concepts, are closely related to metabolic activity and growth of roots.
These functions are indeed important, but it should be kept in mind that roots are highly specialized organs in which numerous syntheses are performed (Mothes, 1956).
226 For a long time the root system was regarded only as an auxiliary organ of the plant providing mechanical fastening in the soil and absorbing water and mineral salts.
Optimal conditions for vigorous root growth are as important for high productivity as are good conditions for shoot growth. THE GROSS ROOT SYSTEM Many investigations on the structure of the root system of trees have been performed during recent decades to get information on the specific peculiarities of root morphology and on the extent of utilization of the soil volume by trees growing on different sites.
Although this has often been said, little is really known in detail. Valuable knowledge was obtained by such static surveys on trees of different ages and on different sites.
The physiology and ecology of root growth are still a neglected segment of plant physiology. By investigating root arrangement and distribution in the soil, practical conclusions were drawn for silviculture and horticulture. Many failures in cultural techniques result from ignorance of the normal course of root growth and of the influences of environmental conditions upon it. This is mainly because of difficulties arising from the methods used.Only some of the most important papers on this subject can be cited here. Page 181 HORST LYR AND GUNTER HOFFMANN At present it is difficult to draw general conclusions from the statements in the literature because environmental conditions and research techniques have varied widely and often have been only inadequately described. Numerous questions are still almost uninvestigated,-for example, the correlative reciprocal effects between root and shoot systems, the influence of environmental factors on the intensity and course of root growth, and specific optimum values for the different tree species.