318 
willows, or by layers, like the Hunting- 
don and Belgian elms. We may resort 
to grafting low on stocks, which should 
be perhaps seedlings of one or other 
parent. This method will serve when 
cuttings and layers are not available. 
It is evident, that, when a valuable 
hybrid has been produced, it can be 
propagated and be put on the market, 
if necessary, without delay.” 
A few suggestions on the technique of 
cross-pollinating trees may be useful 
to those who want to try the artificial 
production of vigorous trees. Both 
HYBRID NUT 
Cross between pecan and 
shellbark hickory, borne 
by the tree shown in 
Fig. 12. The nut is 
natural size, and en- 
closed in its husk, one 
side of which has been 
removed. It is of 
small value, commer- 
cially. Photograph 
from the United States 
Department of Agri- 
culture. (Fig. 15.) 
male and female flowers should be 
protected with bags, in order to prevent 
the possibility of a mix-up in heredity 
through the presence of foreign pollen. 
The male flowers should be bagged < 
week before they shed their sola, 
while the female flowers may be pro- 
tected for a fortnight before the stigmas 
The Journal of Heredity 
are receptive and a week after the cross- 
pollination has been made. If the tree 
with which one is working has perfect 
flowers and is to be used as the seed- 
bearing parent, the pollen-bearing organs 
must of course be removed at an early 
stage, with a needle-pointed forceps. 
This operation is a delicate one, par- 
ticularly if it must be carried out at the 
top of a lofty tree, swaying in the wind. 
Sometimes it may not be necessary, if 
the flowers are protected by nature 
from self-pollination. In the case of 
the ash and elm, for example, the 
stigmas are receptive some days before 
the anthers shed their pollen. Under 
these circumstances, the pollen from 
another species may be applied to the 
stigma, and no attention paid to the 
anthers. 
HANDLING TREE POLLEN 
“Pollen spoils by keeping, but it often 
must be kept for some time till the 
stigma of the female parent is receptive. 
It is often obtained from distant coun- 
tries where trees of the desired species, 
flowering early, can be found. It is best 
kept in a small glass tube either corked 
or plugged with cotton wool. Pollen 
is usually collected by cutting off the 
flowering twigs and placing them on 
white paper in a dry place for one or 
two days. 
“Pollen is applied with a camel’s hair 
brush, and a minute quantity is suffi- 
cient for each stigma. The stigmas are 
to be pollinated when receptive, indi- 
cated by the presence on them of 
sugary solution or by their change to a 
brighter hue. Pollen grains may not 
be able to germinate on the stigma of 
another species, and yet be capable of 
fertilizing it, if germination could be 
induced. The transference of a drop 
of the substance secreted by the stigma 
of the pollen-bearing species to the 
stigma of the other parent might induce 
germination. The best time for pollina- 
tion is in the warm part of the day, 
between 11 a. m. and 3 p. m. in early 
spring. Cold, wet days should be 
avoided.” 
It is not a very long time, in the 
history of the world, since the English 
gardener Fairchild produced the first 
