Another experiment was now tried.  Firstly, plants of the eighth self-fertilised generation were again self-fertilised, producing plants of the ninth self-fertilised generation.  Secondly, two of the plants of the eighth self-fertilised generation were intercrossed one with another, as in the experiment above referred to; but this was now effected on plants which had been subjected to two additional generations of self-fertilisation.  Thirdly, the same plants of the eighth self-fertilised generation were crossed with pollen from plants of a fresh stock brought from a distant garden.  Numerous plants were raised from these three sets of seeds, and grown in competition with one another.  The plants derived from a cross between the self-fertilised plants exceeded in height by a little the self-fertilised, namely, as 100 to 92; and in fertility in a greater degree, namely, as 100 to 73.  I do not know whether this difference in the result, compared with that in the previous case, can be accounted for by the increased deterioration of the self-fertilised plants from two additional generations of self-fertilisation, and the consequent advantage of any cross whatever, along merely between the self-fertilised plants.  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.

4.  Iberis umbellata.