NATIVE WOODY PLANTS OF THE UNITED STATES 33 
species of the rose family will germinate readily if planted at once, 
but if dried will fall into a state of secondary dormancy necessitating 
stratification to assure germination (313). Seed of birches and bass- 
wood germinates much more poorly when permitted to dry out after 
maturity. 
Temperature greatly influences the keeping quality of seed (357). 
For most woody plant seed, 35°-40° F. is considered the best tem- 
perature. At these levels the moisture content may vary somewhat 
without harm to the seed. Freezing should be guarded against. 
Low oxygen content can be obtained by storage in airtight contain- 
ers; this should be watched, since high oxygen content reduces keep- 
ing quality. 
“Stratifying,” as here used, means placing the seed in layers of 
peat and holding them at 35°-40° F. or, in specific instances, at the 
temperature noted in the list under the species. If seed is to be 
stratified, it should first be treated with a disinfectant. Potassium 
permanganate in 5 to 10 percent solution is useful for this purpose. 
All of these operations and also those that follow are treated ad- 
mirably in The Modern Nursery (357). Seeding and Planting in 
the Practice of Forestry (573) treats particularly of tree species. 
Seed may fail to germinate because of incompletely organized 
embryos or hard seed coats, or because certain internal chemical 
changes that must take place before germination have not occurred. 
Additional food in the form of a dilute sugar solution may assist 
embryo organization during stratification. Seeds with hard seed 
coats are treated with hot water or agitated with sharp sand to assist 
them in germinating. Seed requiring a rest period must be stratified 
in the manner described. 
Such of these practices as are known to apply are indicated for 
each species or genus in the list. In addition, data on the number 
of seeds per pound, the germination percentage, and the approxi- 
mate number of usable plants to be expected from each pound of 
seed are given. These notes are intended to assist the technician in 
large-scale operations by giving him some idea of the nursery space 
he may require. Obviously, they can be only approximate. 
The number of seeds per pound depends on individual variation 
in size of seed. This in turn depends on the age and vigor of the 
plant, the fullness of the crop, differences in site of the individual 
plants, and place of collection. Trees on good sites produce larger 
seeds than those on poor ones, and seeds collected at the northern 
extension of the tree range or from higher elevations are usually 
smaller than those collected from the southern part of the range or 
from lower altitudes (573). This is probably true also of shrubs. 
it can thus be seen that the reported number of seeds per pound 
may vary tremendously. However, some indication is better than 
none at all. 
Theoretically, the number of seeds per pound multiplied by the 
percentage of germination should give the number of usable plants 
to be expected per pound of seed. Actually, this is rarely true. Too 
many other factors are involved and the number of usable plants is 
often only one-third to one-fifth or less of the theoretical figure. For 
several hundred species the actual approximate number of usable 
plants per pound of seed, determined empirically in the Section of 
