_Mutual relationship of different species_, with reference especially to their relative height growth and their relative light requirements, must be considered in starting a mixed plantation. Mixed forest plantations (made of several kinds) have so many advantages over pure plantations (made of one kind) that they should be preferred, except for very particular reasons. Mixed plantations are capable of producing larger quantities of better and more varied material, preserve soil conditions hotter, are less liable to damage from winds, fires, and insects, and can be more readily reproduced. The following general rules should guide in making up the composition of a mixed plantation: _a._ Shade-enduring kinds should form the bulk (five-eighths to seven-eighths) of the plantation, except on specially favored soils where no deterioration is to be feared from planting only light-needing kinds, and in which case those may even be planted by themselves. _b._ The light-needing trees should be surrounded by shade-enduring of slower growth, so that the former may not be overtopped, but have the necessary light and be forced by side shade to straight growth. _c._ Shade-enduring species may be grown in admixture with each other when their rate of height growth is about equal, or when the slower-growing kind can be protected against the quicker-growing (for instance, by planting a larger proportion of the former in groups or by cutting back the latter). _d._ The more valuable timber trees which are to form the main crop should be so disposed individually, and planted in such numbers among the secondary crop or nurse crop, that the latter can be thinned out first without disturbing the former. Where a plantation of light-foliaged trees has been made (black walnut, for instance), it can be greatly improved by "under-planting" densely with a shade-enduring kind, which will choke out weed growth, improve the soil, and thereby advance the growth of the plantation. The selection and proper combination of species with reference to this mutual relationship to each other and to the soil are the most important elements of success. _Availability_ of the species also still needs consideration in this country; for, although a species may be very well adapted to the purpose in hand, it may be too difficult to obtain material for planting in quantity or at reasonable prices. While the beech is one of the best species for shade endurance, and hence for soil cover, seedlings can not be had as yet in quantity. Western conifers, although promising good material for forest planting, are at present too high priced for general use. Some eastern trees can be secured readily--either their seed or seedlings--from the native woods; others must be grown in nurseries before they can be placed in the field.