On the other hand, a cross between two varieties of the pea
causes a marked superiority in the growth and vigour of the offspring,
over the self-fertilised plants of the same varieties, as shown by two
excellent observers. From my own observations (not made with great care)
the offspring from crossed varieties were to self-fertilised plants in
height, in one case as 100 to about 75, and in a second case as 100 to
60.
8. Lathyrus odoratus.
The sweet-pea is in the same state in regard to self-fertilisation as
the common pea; and we have seen that seedlings from a cross between two
varieties, which differed in no respect except in the colour of their
flowers, were to the self-fertilised seedlings from the same
mother-plant in height as 100 to 80; and in the second generation as 100
to 88. Unfortunately I did not ascertain whether crossing two plants of
the same variety failed to produce any beneficial effect, but I venture
to predict such would be the result.
9. Petunia violacea.
The intercrossed plants of the same stock in four out of the five
successive generations plainly exceeded in height the self-fertilised
plants. The latter in the fourth generation were crossed by a fresh
stock, and the seedlings thus obtained were put into competition with
the self-fertilised plants of the fifth generation. The crossed plants
exceeded the self-fertilised in height in the ratio of 100 to 66, and in
weight as 100 to 23; but this difference, though so great, is not much
greater than that between the intercrossed plants of the same stock in
comparison with the self-fertilised plants of the corresponding
generation.
Pages:
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391