Darwin accepted these observations as correct, and endeavoured to explain them as due to a migration of his 'gemmules' from the fertilized ovum into the surrounding tissue of the mother-plant. His explanation was not correct, we can say with confidence now, but he was right so far, for the phenomena of Xenia do occur; they are not illusory as most modern botanists seem inclined to believe. I myself was at first inclined to wait for further facts in proof that the phenomena of Xenia really occurred before attempting to bring them into harmony with my theory, and this will not be found fault with when it is remembered that these cases of Xenia seem to stand in direct contradiction to the fundamental postulates of the germ-plasm theory. For this depends essentially on a definite stable structure of the germ-substance, which lies within the nucleus in the form of chromosomes, and which cannot pass from one cell to another in any other way than by cell-division and division of the nucleus; how then could it pass from the fertilized ovum to the cells of the endosperm which do not derive their origin from it at all, but from other cells of the embryo-sac? In point of fact some of my opponents have cited Xenia as an actual refutation of my theory. [Illustration: FIG. 82. Fertilization in the Lily (_Lilium martagon_), after Guignard. _A_, the embryo-sac before fertilization; _sy_, synergidæ; _eiz_, ovum; _op_ and _up_, upper and lower 'polar nuclei'; _ap_, antipodal cells. _B_, the upper part of the embryo-sac, into which the pollen-tube (_pschl_) has penetrated with the male sex-nucleus (♂_k_) and its centrosphere; below that is the ovum-nucleus (♀_k_) with its (also doubled) centrosphere (_csph_). _C_, remains of the pollen-tube (_pschl_); the two sex-nuclei are closely apposed. Highly magnified.]