770 LECTURE XLIII. 



proceed may be recognised from the material peculiarity of their contents, at a 

 time when the surrounding tissue still possesses entirely the character of the so-called 

 primary meristem, or embryonic tissue of the growing-point. The diflferentiation 

 of the two sexual products thus begins in the interior of growing-points, and 

 the product of the sexual union is an embryo whose tissue is identical witli 

 that of a growing-point, and from which the first growing-points of the new plant 

 are to be derived as remnants. Thus, strictly speaking, sexual reproduction is 

 no more calculated to produce a new organism than is asexual reproduction; 

 the elements from which the embryo arises are simply products of the embryonic 

 substance of a previous plant, and finally, we may say, that what has since the 

 beginning of organic life on the earth continually maintained itself alive amidst the 

 perpetual change of all forms, in the continuous alternation of life and death, 

 and has continually regenerated itself, is the embryonic substance of the growing- 

 points, which in certain cases becomes differentiated into male and female, and 

 these unite again subsequently. In these extremely minute masses of matter, organic 

 life has continually maintained itself through the slow course of geological epochs ; 

 those parts of the plant which present themselves directly to the eye— fully 

 grown roots, shoot-axes, leaves, woody-masses, &c. — all these are products of that 

 embryonic substance which is continually regenerating itself. These, its products, 

 it is true outweigh it in mass a million-fold, but they are not capable of regeneratiorii 

 It is not in these that the continuity of organic life is 'maintained, but it is 

 these, which by means of their work in common, carry on the processes of 

 assimilation and metabolism, and a very small quantity of the substance which 

 they do not themselves employ for their growth, is made use of for the nutrition 

 of the embryonic substance of the growing-points and sexual cells. 



After this probably not entirely superfluous digression I now return to my 

 theme, the mutual interaction of the sexual cells, resuming the discussion from another 

 side. The reasons have already been given which impel us to the assumption 

 that in order to make the oosphere fertile, some substance on the part of the male 

 cells must be added to it which it wanted previously. The most recent investiga- 

 tions of Schmitz, Strasburger, Zacharias, and others, lead in the first place to 

 the result that the fertilising substance is to be sought in the nuclear substance, the 

 nuclein of the male cell. It appears, according to the observers mentioned, to he 

 established as regards zoosperms (antherozoids), that their proper body is formed from 

 the nuclein of the mother-cell, while the part which bears the cilia appears to proceed 

 from the protoplasm. The nucleus of the mother-cell of the antherozoid enlarges until 

 it has taken up into itself the whole of the protoplasm of the cell, or nearly so. 

 The peripheral layer then condenses into an annular or spirally inroUed band, while 

 the central portion becomes less dense and constitutes the vesicle which newly 

 escaped antherozoids usually trail at their hinder ends, but which they often soon 

 lose. Zacharias has attempted to establish by microchemical methods that the 

 actual body of the antherozoid is identical with nuclein, and has pointed out that 

 in this respect animals agree entirely with plants. 



Thus what is carried into the oosphere by the antherozoids is nuclein, since 

 we may believe that the only importance of the cilia (which do not consist of 

 nuclein) is simply that of motile organs. 



