The innate power of the crossed plants to resist unfavourable conditions far better than did the self-fertilised plants, was shown on two occasions in a curious manner, namely, with Iberis and in the third generation of Petunia, by the great superiority in height of the crossed over the self-fertilised seedlings, when both sets were grown under extremely unfavourable conditions; whereas owing to special circumstances exactly the reverse occurred with the plants raised from the same seeds and grown in pairs in pots.  A nearly analogous case was observed on two other occasions with plants of the first generation of Nicotiana.

The crossed plants always withstood the injurious effects of being suddenly removed into the open air after having been kept in the greenhouse better than did the self-fertilised.  On several occasions they also resisted much better cold and intemperate weather.  This was manifestly the case with some crossed and self-fertilised plants of Ipomoea, which were suddenly moved from the hothouse to the coldest part of a cool greenhouse.  The offspring of plants of the eighth self-fertilised generation of Mimulus crossed by a fresh stock, survived a frost which killed every single self-fertilised and intercrossed plant of the same old stock.  Nearly the same result followed with some crossed and self-fertilised plants of Viola tricolor.  Even the tips of the shoots of the crossed plants of Sarothamnus scoparius were not touched by a very severe winter; whereas all the self-fertilised plants were killed halfway down to the ground, so that they were not able to flower during the next summer.  Young crossed seedlings of Nicotiana withstood a cold and wet summer much better than the self-fertilised seedlings.  I have met with only one exception to the rule of crossed plants being hardier than the self-fertilised:  three long rows of Eschscholtzia plants, consisting of crossed seedlings from a fresh stock, of intercrossed seedlings of the same stock, and of self-fertilised ones, were left unprotected during a severe winter, and all perished except two of the self-fertilised.  But this case is not so anomalous as it at first appears, for it should be remembered that the self-fertilised plants of Eschscholtzia always grow taller and are heavier than the crossed; the whole benefit of a cross with this species being confined to increased fertility.

Independently of any external cause which could be detected, the self-fertilised plants were more liable to premature death than were the crossed; and this seems to me a curious fact.  Whilst the seedlings were very young, if one died its antagonist was pulled up and thrown away, and I believe that many more of the self-fertilised died at this early age than of the crossed; but I neglected to keep any record.  With Beta vulgaris, however, it is certain that a large number of the self-fertilised seeds perished after germinating beneath the ground, whereas the crossed seeds sown at the same time did not thus suffer.