Going still further, we may compare the effects of cross-breeding or of hybridisation, where the _progeny_ show that changes have resulted from the mutual interactions and reactions of the commingled protoplasm, with Daniel's results, in which he obtains proof of such interactions of the commingled protoplasmic cell-contents of grafts in the seedling progeny; although there is no probability--we may even say possibility--in this latter case that the effects are due to nuclear fusions, but only that the germ-plasm of the seed-bearing plant has been affected by the changes in the cell-protoplasm which nourishes it when the reproductive cells are forming. In the case of graft-hybrids the matter appears to be somewhat different, and we may well suppose, with Strasburger, that the commingling of characters observed in flowers, fruits, foliage, etc., on shoots borne after grafting are due to the occurrence of nuclear fusions during the union of the grafted tissues; though it is by no means impossible that what has really happened is profound alterations in the nuclear substance (germ-plasm) owing to its being nourished by cell-protoplasm (somato-plasm) which has been itself affected by the interchanges of substance between scion and stock, and therefore itself furnishes a different nutrient medium from the unaltered cytoplasm of either. But even here we can find parallels among the ordinary phenomena of plant reproduction. Maize plants with white endosperm containing starch, if crossed by pollen from other plants with purple endosperm containing sugar, bear seeds with purple endosperm containing sugar, and such _Xenia_ may be compared to graft-hybrids in many respects. I know of no case among fungus infections which could be compared directly with these examples, and it is not at all likely that we shall meet with any instance of a fungus-hypha handing over nuclear substance to an egg-cell, and so affecting the latter that an embryo results. But the case is not hypothetically impossible, although the distant relationships of the two groups of organisms render it extremely improbable among the higher plants. It is by no means so improbable, however, that further research may show cases where the egg-cell of a lower cryptogam--_e.g._ another fungus--may be affected either directly, or indirectly, by the protoplasm of a parasitic or symbiotic hypha, as suggested by the extraordinary phenomena of symbiosis. Some of the variations in grafted plants are found to predispose the plant to disease, or the reverse, and cases may be cited where the resulting shoots, foliage, or fruits, or seedlings more readily fall a prey to, or resist, parasitic fungi and insects than the ungrafted plants. Daniel gives instances of such--_e.g._ among other examples, Peas grafted on Beans yield seeds which suffer more from Erysipheae than the normal seedlings. But the best known cases are those of Vines in their relations to _Phylloxera_, already referred to (p. 155).