104 Principles of Plant Culture. 
but the seeds of most annual and biennial plants may be- 
come air-dry without material loss of vitality. The seeds 
of very many sbrubs and trees, however, lose vitality rapidly 
by such drying, and, of some species, are destroyed by it. In 
nature, seeds of the latter class are usually dropped from 
the parent plant before becoming dry, and are soon covered 
with leaves or other litter that keep them moist. Nursery- 
men either plant such seeds as soon as they are ripe, or else, 
if of species that do not germinate as soon as ripe, they im- 
itate nature by the process known as 
170. Stratification of Seeds. This consists in mixing 
the freshly-gathered seeds with moist sand, taking care that 
the sand is kept moist until the time for sowing arrives. 
Large quantities of seeds may be stratified in boxes, by 
placing the moist sand and seeds in alternate layers, or 
the layers may be built up ina pile on the ground. The 
sand should be coarse enough to admit some passage of air 
between the particles, and to give perfect drainage. The 
layers should not much exceed an inch in thickness, except 
for the larger seeds, and the number of layers should not 
be so large as to prevent proper aeration of the mass. Small 
quantities of seeds may be mixed with sand or porous loam, 
in flower-pots. Moisture may be maintained in the boxes or 
pots by burying them a foot or more deep in the soil, in a 
well-drained place, or by storing them in a moist cellar. 
Care is necessary to keep mice and other vermin from strat- 
ified seeds. It is well to cover pots in which valuable seeds 
are stratified, with a sheet of tin or zinc, and metal labels 
are best for distinguishing different sorts of seed. The 
seeds should remain stratified until sowing time, when they 
may be sifted out of the soil, or sown with it, as is more 
