83, and the self-fertilised 30.16 inches; or as 100 to 92.
20. COMPOSITAE.--Lactuca sativa. (5/19. The Compositae are well-adapted
for cross-fertilisation, but a nurseryman on whom I can rely, told me
that he had been in the habit of sowing several kinds of lettuce near
together for the sake of seed, and had never observed that they became
crossed. It is very improbable that all the varieties which were thus
cultivated near together flowered at different times; but two which I
selected by hazard and sowed near each other did not flower at the same
time; and my trial failed.)
Three plants of Lettuce (Great London Cos var.) grew close together in
my garden; one was covered by a net, and produced self-fertilised seeds,
the other two were allowed to be naturally crossed by insects; but the
season (1867) was unfavourable, and I did not obtain many seeds. Only
one crossed and one self-fertilised plant were raised in Pot 1, and
their measurements are given in Table 5/66. The flowers on this one
self-fertilised plant were again self-fertilised under a net, not with
pollen from the same floret, but from other florets on the same head.
The flowers on the two crossed plants were left to be crossed by
insects, but the process was aided by some pollen being occasionally
transported by me from plant to plant. These two lots of seeds, after
germinating on sand, were planted in pairs on the opposite sides of Pots
2 and 3, which were at first kept in the greenhouse and then turned out
of doors.
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