CONTRIBUTIONS FROM THE WISLEY LABORATORY. 355 
mentioned in the report of the John Innes Horticultural Institute* — 
the results of some of which we have duplicated. In 1919 20 flowers 
of President were crossed with Late Orange, and no fruit was set, 
and again in 1920 106 flowers were pollinated in the same way 
and no fruit was set, whilst other crosses on the same tree set 
well. This is probably another case of "cross incompatibility." 
These are the only exceptions found so far in plums, and except for 
these special cases any one variety has been found to fertilize any 
other that has been tried. 
The majority of plums are in flower at much about the same time, 
so that almost any varieties, with the exceptions just mentioned, may 
be planted together and successful cross-pollination take place. 
The following table shows the eighteen varieties mentioned in this 
paper in their order of flowering, under orchard conditions at Wisley, for 
the years i9o8-io-ii-i2-i4-i7-i9-20i and it will be seen from this 
that the latest is in flower 7 days after the earhest, whilst the average 
is less than 4 days. It is found that the different varieties are in flower 
from 14-24 days, and in full bloom on about the eighth day after 
commencing to flower, so that there is a considerable overlapping 
period with all. 
Order of Flowering. f 
Grand Duke earliest — no definite records, 
o Monarch. 
1- 4 Jefferson's. 
2*5 Denniston's Superb. 
2- 5 Coe's Goldeii Drop. 
2-7 President. 
3 Early Rivers. 
3 • 5 Decaisne. 
4 Late Orange. 
4*3 Comte d'Althan's Gage. 
4*8 Kirke's Blue. 
5 The Czar. 
5 Pond's Seedling. 
5 '5 Transparent Gage. 
5 •5 Washington. 
6 Prince Engelbert. 
6*5 Late Transparent Gage. 
7-5 Stint. 
As a control to the percentage of fruit setting in the orchard house, 
trees were chosen outside growing under orchard conditions, and a 
number of flowers counted and the branches labelled to see the per- 
centage setting under normal conditions ; counts were made at two 
different dates — the first at about six weeks after flowering, and the 
second five weeks after the first count, with the following results : 
Variety. 
Bittern . 
Blue Rock 
Coe's Golden Drop 
Denniston's Superb (i) 
(2) 
Victoria . 
Total . 
No. Flowers counted. 
I branch 
612 flowers 
234 
145 
322 „ 
300 
660 
395 " 
250 ,. 
142 „ 
3060 
ist Count. 
2nd Count. 
153 fruits 
105 „ 
44 
112 ,, 
223 
178 
128 „ 
173 
80 .. 
I 47 fruits 
I 34 
24 
49 
i 103 
61 „ 
i 70 
36 
1 1 96 439 
39 per cent. 1 14 per cent. 
* Sutton, I., in Journ. of Genetics, VII. Aug. 1918. 
t The figures preceding the name represent the average number of days at 
which flowering commenced after ' Monarch ' began to flower. 
