In fact there are analogies between grafting and parasitism which cannot be overlooked, and should not be underestimated, their commonest expression appearing in the alterations in stature, habit, period of ripening, and so forth. These analogies are easily apprehended when we compare parasites like the Mistletoe, _Loranthus_, or even such root-parasites as the Broom-rapes and the Rhinanthoideae with grafts; but they also exist in the case of many fungus-parasites, and we might almost as accurately speak of _grafting_ some fungi on their hosts as of _infecting_ the latter with them, especially when it is borne in mind that the effect of the scion on the stock is by no means always to the benefit of the latter, and that there are reasons for regarding the action of some such unions as that of a sort of slow poisoning of the stock by the scion. Why do we not here say that the stock has been _infected_ by the scion? The resemblances between pollination and the infection by fungus hyphae may also be insisted upon. If we take into account Darwin's remarkable experiments showing that in "illegitimate unions" the pollen exerts a sort of poisonous action on the stigmas or ovules, it is possible to arrange a series of cases starting with perfectly legitimate pollinations where the pollen tube feeds as it descends the style on materials provided by the cells, and proceeding to cases where the pollen is more and more merely just able to penetrate the ovary and reach the ovules, to the extreme cases where no union at all is possible. Side by side with such series could be arranged analogous cases where fungus spores can enter and infect the cells of the host, and live symbiotically with or even in them, or can penetrate only with difficulty, or with poisonous effects, and finally cannot infect the plant at all. Less obviously, but nevertheless existing, are gradations in grafting to be observed, where one and the same stock may be successfully combined with a scion which improves it--or which is improved by it--or the scion may unite but acts injuriously on it, or, finally, cannot be induced to unite. But we may go further than this in these comparisons. Just as the results of pollination frequently induce far-reaching effects on distant tissues--_e.g._ the swelling of Orchid ovaries, and rapid fading of the floral organs--so also the effects of hyphae in the tissues may induce hypertrophies, deflection of nutrient materials, and the atrophy of distant parts--_e.g._ the curious phenomena observed in _Euphorbia_ attacked by _Uromyces_--and some of the distant actions in grafts may be compared similarly.