7 page 467.) If we take into account of the fact that a much greater proportion of flowers produced capsules when crossed than when self-fertilised, the relative fertility of the crossed to the self-fertilised flowers was as 100 to 52. Nevertheless these plants, whilst still protected by the net, spontaneously produced a considerable number of self-fertilised capsules.

The seeds of the two lots after germinating on sand were planted in pairs on the opposite sides of four large pots. At first there was no difference in their growth, but ultimately the crossed seedlings exceeded the self-fertilised considerably in height, as shown in Table 4/34. But I believe from the cases which follow that this result was accidental, owing to only a few plants having been measured, and to one of the self-fertilised plants having grown only to a height of 15 inches. The plants had been kept in the greenhouse, and from being drawn up to the light had to be tied to sticks in this and the following trials. They were measured to the summits of their flower-stems.

TABLE 4/34. Eschscholtzia californica.

Heights of Plants to the summits of their flower-stems measured in inches.

Column 1: Number (Name) of Pot.

Column 2: Crossed Plants.

Column 3: Self-fertilised Plants.

Pot 1 : 33 4/8 : 25.

Pot 2 : 34 2/8 : 35.

Pot 3 : 29 : 27 2/8.

Pot 4 : 22 : 15.

Total : 118.75 : 102.25.

The four crossed plants here average 29.68 inches, and the four self-fertilised 25.56 in height; or as 100 to 86. The remaining seeds were sown in a large pot in which a Cineraria had long been growing; and in this case again the two crossed plants on the one side greatly exceeded in height the two self-fertilised plants on the opposite side. The plants in the above four pots from having been kept in the greenhouse did not produce on this or any other similar occasion many capsules; but the flowers on the crossed plants when again crossed were much more productive than the flowers on the self-fertilised plants when again self-fertilised. These plants after seeding were cut down and kept in the greenhouse; and in the following year, when grown again, their relative heights were reversed, as the self-fertilised plants in three out of the four pots were now taller than and flowered before the crossed plants.

CROSSED AND SELF-FERTILISED PLANTS OF THE SECOND GENERATION.

The fact just given with respect to the growth of the cut-down plants made me doubtful about my first trial, so I determined to make another on a larger scale with crossed and self-fertilised seedlings raised from the crossed and self-fertilised plants of the last generation. Eleven pairs were raised and grown in competition in the usual manner; and now the result was different, for the two lots were nearly equal during their whole growth. It would therefore be superfluous to give a table of their heights. When fully grown and measured, the crossed averaged 32.47, and the self-fertilised 32.81 inches in height; or as 100 to 101. There was no great difference in the number of flowers and capsules produced by the two lots when both were left freely exposed to the visits of insects.

PLANTS RAISED FROM BRAZILIAN SEED.

Fritz Muller sent me from South Brazil seeds of plants which were there absolutely sterile when fertilised with pollen from the same plant, but were perfectly fertile when fertilised with pollen from any other plant. The plants raised by me in England from these seeds were examined by Professor Asa Gray, and pronounced to belong to E. Californica, with which they were identical in general appearance. Two of these plants were covered by a net, and were found not to be so completely self-sterile as in Brazil. But I shall recur to this subject in another part of this work. Here it will suffice to state that eight flowers on these two plants, fertilised with pollen from another plant under the net, produced eight fine capsules, each containing on an average about eighty seeds. Eight flowers on these same plants, fertilised with their own pollen, produced seven capsules, which contained on an average only twelve seeds, with a maximum in one of sixteen seeds.

The Effects of Cross and Self-Fertilisation in the Vegetable Kingdom Page 56

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Charles Darwin

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