32 BULLETIN 24, U. S. DEPARTMENT OF AGRICULTURE. 
windfall and breakage. If in the end two seed trees remained to 
even 3 acres, reproduction should be excellent. Since seed is borne 
in abundance each year, the trees will rarely be needed for longer 
than a year or two. One seed tree per acre would be equivalent to 
leaving parallel rows about 600 feet apart, with the trees approxi- 
mately 50 feet apart in the rows. 
In reserving seed trees the following considerations should be 
taken into account: 
(za) Only female trees should be selected for seed production. 
Unfortunately, there seem to be no characteristics other than the 
flowers by which male and female trees may be readily distinguished. 
Seed trees should therefore be marked during the flowering or seed- 
bearing season. The flowers of the seed-producing trees are not 
conspicuous. . They occur in the form of slender catkins, 6 to 10 
inches long, on which the budlike flowers appear very small and 
scattered. During the seeding time the abundance of light “ cotton ” 
- shed by these female catkins readily distinguishes the seed-bearing 
trees. The flowers of the male trees are. on the other hand. more 
showy—bright red or yellow in color—and the catkin fuller, wider, 
and denser. but not as long as the female catkin. 
(6) In addition to one seed tree per acre, a number of male trees 
should also be left in order to insure proper fertilization of the female 
flowers. Fertilization is believed to be effected usually by insects, 
which carry the pollen from the staminate to the pistillate flowers. 
About every fourth tree should be a staminate one. 
(c) Seed trees as far as possible should be the least merchantable 
individuals, since in this way the investment represented by the 
stumpage value of the trees left after logging is the least, whether 
they are later removed or not. Seed trees, however, should be thrifty 
and vigorous. Crooked, forked, or branchy trees, which would cut 
out a comparatively small amount of high-grade lumber, are usually 
Just as vigorous and as suitable for seed production as the tall, clear, 
straight individuals. In fact, the larger the crown, the more seed 
is produced. | 
(Z7) Only windfirm trees should be left. On low, wet sites, where 
the soil is loose and soft, no seed trees should be reserved. 
(€) Seed trees should be removed as soon as possible after young 
growth has become established, otherwise the shade will check the 
growth of many of the younger trees. There is less injury to the 
young growth if the seed trees are cut and removed before it attains 
much size. Since cottonwood often grows at the start at the rate of 
from 5 to 7 feet a year, it is advisable to cut the seed trees the year 
the young growth is established. If for any reason they can not be 
profitably removed and are likely to deteriorate before the next 
lumbering operation, it may sometimes be advisable to deaden them 
