CONTRIBUTIONS FROM THE WISLEY LABORATORY. 353 
CONTRIBUTIONS FROM THE WISLEY LABORATORY. 
XXXVI. — Pollination in Orchards (iv.).* 
Self -Fertility and Self -Sterility in Plums. 
By A. N. Rawes. 
This paper is a preliminary account of the investigations being 
made at Wisley into the self-fertiHty and self-sterility of the many 
varieties of plums. 
The work was commenced in 1919, and was carried out on pot 
trees in an orchard house set aside for experiments relating to fruit 
pollination. The house is specially constructed for this purpose, and 
by means of mosquito bars over the ventilators and double doors 
all insects are excluded, and the danger of disturbance from other 
agencies reduced to a minimum. Two trees of each variety are 
tested in each case, so that the results are duplicated and not subject 
to any abnormalities any one tree may be temporarily suffering from. 
Each flower is hand-polHnated, and both in the case of crossed and 
selfed flowers pollination is done by means of ripe stamens carried 
in a pair of forceps and brushed on the stigmas of the flowers to 
be pollinated. This is believed to be a more accurate and satisfac- 
tory method of pollination than by the use of the camel-hair brush. 
All flowers to be crossed are emasculated before their stamens are ripe 
or the petals open. 
Usually the stigma of the plum flower is in a receptive condition, 
i.e. sticky, a day or two before the stamens are ripe, but this not 
always so and in some cases both stamens and stigma " ripen " at the 
same time, whilst in other cases the stamens are occasionally found 
ripe a day before the stigmas become receptive. 
So far eighteen varieties have been tested as to whether they are 
able to set fruit when pollinated with their own pollen or not, and 
out of this number — 
eleven varieties were found to be self -sterile, 
three varieties were found to be self -fertile, 
and four varieties were found partly self -fertile. 
In the first table on p. 354 are the data from which these con- 
clusions are arrived at. 
omparison between crossed and selfed fruits from a self-fertile 
variety showed no difference, due to the foreign pollen, either in the size 
c :"iape of the fruit or stone ; neither was there any difference in the 
♦ For previous articles see R.H.S. Journal, 37, p. 350 and 39, p. 366 and 
p. 615. 
VOL. XLVI. 2 A 
