But however this may
be, the effects of crossing the self-fertilised plants of the eighth
generation with a fresh stock were extremely striking; for the seedlings
thus raised were to the self-fertilised of the ninth generation as 100
to 52 in height, and as 100 to 3 in fertility! They were also to the
intercrossed plants (derived from crossing two of the self-fertilised
plants of the eighth generation) in height as 100 to 56, and in
fertility as 100 to 4. Better evidence could hardly be desired of the
potent influence of a cross with a fresh stock on plants which had been
self-fertilised for eight generations, and had been cultivated all the
time under nearly uniform conditions, in comparison with plants
self-fertilised for nine generations continuously, or then once
intercrossed, namely in the last generation.
3. Brassica oleracea.
Some flowers on cabbage plants of the second self-fertilised generation
were crossed with pollen from a plant of the same variety brought from a
distant garden, and other flowers were again self-fertilised. Plants
derived from a cross with a fresh stock and plants of the third
self-fertilised generation were thus raised. The former were to the
self-fertilised in weight as 100 to 22; and this enormous difference
must be attributed in part to the beneficial effects of a cross with a
fresh stock, and in part to the deteriorating effects of
self-fertilisation continued during three generations.
Pages:
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387