14 MISC. PUBLICATION 303, U. S. DEPT. OF AGRICULTURE 
should be those that have already been tested for such a site; that is, 
species native to the region in question. Our second choice should be 
species that are not native; that is, exotic or introduced plants. If it 
is certainly known that there is no native species that can grow on a 
chosen site, then we are justified in turning to exotic forms. Clements 
(121, ». 360) summarized this: “* * * nature is to be followed as 
closely as possible, and hence native materials alone are to be employed, 
preferably from the outset, but invariably in the final composition.” 
Chapman (7/8) claims further that until additional data can be ob- 
tained we are justified in making large-scale plantings only on the 
basis of ecological principles apphed to the native species of the region. 
This should not be interpreted to mean that the introduction of a 
foreign species is inherently undesirable. It is recognized, of course, 
that the introduction of some non-native woody species has already 
been successfully accomplished, and these are excepted from the pre- 
ceding statements. But large-scale plantings should be limited to 
species proved to be adaptable to a given area and known to be able 
to compete with plants that now largely occupy the territory. In 
forest planting, Toumey and Korstian (573) characterize the selec- 
tion of exotics and species from widely diiferent regions as very 
hazardous. In ornamental planting, where each plant is protected 
and given special protection, the use of exotics may be justified, but 
unless actual experimental plantings have been made or unless site 
factors can definitely be shown to be similar to those of the region 
from which the species is introduced, exotic species should be ex- 
cluded from forest crops. The extensive use of Scotch pine and 
Norway spruce for instance, in the eastern United States is much to 
be regretted in the opinion of these workers, since results from such 
use are still problematical. 
FRUIT PRODUCTION 
Wherever dioecious species are used, if fruit production is desired, 
a few staminate (pollen-bearing) plants must be included in the 
planting. Monoecious plants, on the other hand, since both staminate 
and pistillate fiowers are present on each bush, necessitate no such 
precaution. Examples of dioecious plants include Baccharis, Ilex, 
Maclura, Myrica, Shepherdia, Taxus, and some species of Juniperus. 
There are, in addition, some species that are partly dioecious, that 
is, some of the plants may be entirely staminate and some slightly 
polygamous. In the latter, sufficient staminate flowers are present on 
pistillate plants to ensure reasonably complete fertilization. The 
genera Celastrus, Ailanthus, Morus, Rhus, and Vitis, furnish species 
of this sort (679). With these, the addition of staminate forms to 
a planting may often be advantageous although not always necessary. 
At present there is no way to distinguish readily the seeds that 
will produce staminate from those that will produce pistillate plants. 
Therefore, to ensure getting fruit-bearing plants it may be necessary 
to use cuttings only, selecting them mainly from pistillate plants. In 
reproducing such plants from seed, the proportion of staminate to 
pistillate plants is often unknown. 
Other sorts of dioecism are known. Perfect flowers may often 
produce pollen that for various reasons may be more or less incapable 
