some other species, which had been intentionally treated by me in this manner; yet we know that these species in their normal condition profit greatly by being intercrossed.  There is, therefore, not a single case in Table 7/A which affords decisive evidence against the rule that a cross between plants, the progenitors of which have been subjected to somewhat diversified conditions, is beneficial to the offspring.  This is a surprising conclusion, for from the analogy of domesticated animals it could not have been anticipated, that the good effects of crossing or the evil effects of self-fertilisation would have been perceptible until the plants had been thus treated for several generations.

The results given in Table 7/A may be looked at under another point of view.  Hitherto each generation has been considered as a separate case, of which there are eighty-three; and this no doubt is the more correct method of comparing the crossed and self-fertilised plants.

But in those cases in which plants of the same species were observed during several generations, a general average of their heights in all the generations together may be made; and such averages are given in Table 7/A; for instance, under Ipomoea the general average for the plants of all ten generations is as 100 for the crossed, to 77 for the self-fertilised plants.  This having been done in each case in which more than one generation was raised, it is easy to calculate the average of the average heights of the crossed and self-fertilised plants of all the species included in Table 7/A.  It should however be observed that as only a few plants of some species, whilst a considerable number of others, were measured, the value of the mean or average heights of the several species is very different.  Subject to this source of error, it may be worth while to give the mean of the mean heights of the fifty-four species in Table 7/A; and the result is, calling the mean of the mean heights of the crossed plants 100, that of the self-fertilised plants is 87.  But it is a better plan to divide the fifty-four species into three groups, as was done with the previously given eighty-three cases.  The first group consists of species of which the mean heights of the self-fertilised plants are within five per cent of 100; so that the crossed and self-fertilised plants are approximately equal; and of such species there are twelve about which nothing need be said, the mean of the mean heights of the self-fertilised being of course very nearly 100, or exactly 99.58.  The second group consists of the species, thirty-seven in number, of which the mean heights of the crossed plants exceed that of the self-fertilised plants by more than five per cent; and the mean of their mean heights is to that of the self-fertilised plants as 100 to 78.  The third group consists of the species, only five in number, of which the mean heights of the self-fertilised plants exceed that of the crossed by more than five per cent; and here the mean of the