Owing to the varieties having been self-fertilised for many generations, and to their having been subjected in each generation to nearly the same conditions (as will be explained in a future chapter) I did not expect that a cross between two such plants would benefit the offspring; and so it proved on trial.  In 1867 I covered up several plants of the Early Emperor pea, which was not then a very new variety, so that it must already have been propagated by self-fertilisation for at least a dozen generations.  Some flowers were crossed with pollen from a distinct plant growing in the same row, and others were allowed to fertilise themselves under a net.  The two lots of seeds thus obtained were sown on opposite sides of two large pots, but only four pairs came up at the same time.  The pots were kept in the greenhouse.  The seedlings of both lots when between 6 and 7 inches in height were equal.  When nearly full-grown they were measured, as in Table 5/57.

Table 5/57.  Pisum sativum.

Heights of plants measured in inches.

Column 1:  Number (Name) of Pot.

Column 2:  Crossed Plants.

Column 3:  Self-fertilised Plants.

Pot 1 :  35 :  29 6/8.

Pot 2 :  31 4/8 :  51. 
Pot 2 :  35 :  45. 
Pot 2 :  37 :  33.

Total :  138.50 :  158.75.

The average height of the four crossed plants is here 34.62, and that of the four self-fertilised plants 39.68, or as 100 to 115.  So that the crossed plants, far from beating the self-fertilised, were completely beaten by them.

There can be no doubt that the result would have been widely different, if any two varieties out of the numberless ones which exist had been crossed.  Notwithstanding that both had been self-fertilised for many previous generations, each would almost certainly have possessed its own peculiar constitution; and this degree of differentiation would have been sufficient to make a cross highly beneficial.  I have spoken thus confidently of the benefit which would have been derived from crossing any two varieties of the pea from the following facts:  Andrew Knight in speaking of the results of crossing reciprocally very tall and short varieties, says, “I had in this experiment a striking instance of the stimulative effects of crossing the breeds; for the smallest variety, whose height rarely exceeded 2 feet, was increased to 6 feet; whilst the height of the large and luxuriant kind was very little diminished.” (5/15.  ‘Philosophical Transactions’ 1799 page 200.) Recently Mr. Laxton has made numerous crosses, and everyone had been astonished at the vigour and luxuriance of the new varieties which he has thus raised and afterwards fixed by selection.  He gave me seed-peas produced from crosses between four distinct kinds; and the plants thus raised were extraordinarily vigorous, being in each case from 1 to 2 or even 3 feet taller than the parent-forms,