CONTINUITY OF EMBRYONIC SUBSTANCE. 769 



begin and accomplish further development, and it might almost appear as if our 

 preceding considerations were completely invalidated by this fact. However, the 

 logical conclusion seems to be this : since the asexual spores germinate without 

 fertilisation they simply contain all that is necessary. They do not, as is 

 the case with the oosphere, lack something which must be first transferred 

 to them in order that they may become capable of development ; they do not 

 need fertilisation because they have all they require, and exactly the same con- 

 clusion may be also employed in the very rare cases of well-established Par- 

 thenogenesis and Apogamy, where female reproductive organs arise and are able 

 to form embryos without being fertilised. Here again we may say, since they 

 are able to do this they contain in themselves all that is necessary for 

 development, and if this is the case such female organs are also only apparently 

 female ; since this term should probably be reserved strictly for those cases 

 where a cell is stimulated to further development only by fertilisation. Those 

 cells which do not need fertilisation, such as the spores and gemmae of Muscinese, 

 the conidia of Fungi, and the asexual spores of many Algae, and which give rise to new 

 plants, resemble in this point ordinary vegetative cells, which in fact are also able 

 under favourable circumstances generally to give rise to new plants. 



The question is thus, how comes it that sooner or later in the course of 

 development certain cells are produced which have lost the capacity for further 

 development, per se, but which are therefore in a condition to afford by means 

 of the union of their substance a product capable in the highest degree of 

 development. That this is no incidental occurrence, but must be dependent on 

 something in the deepest being of the organism, I conclude from the elaborate pre- 

 parations for the attainment of the given purpose, since we may regard the formation 

 of the various sexual organs in which the sexual cells eventually arise as such 

 a preparation, — and the higher the organisation the more comprehensive this 

 preparation for the development of sexual cells appears to be — this segregation of the 

 organic constructive substances into two different substances, male and female, which 

 onl}' }ield a vegetative product subsequently by means of their union. 



I have already repeatedly taken opportunities of mentioning the hitherto 

 much too little noticed fact, that the continuity of plant-life is expressed essentially 

 in the continuity of the embryonic substance. I have set forth in detail that in the 

 normal course of the life of a plant, even of a tree which lives hundreds of years, 

 the newly formed growing-points are always the descendants of preceding growing- 

 points, and that finally all the numerous but small growing-points of a much- 

 branched plant are derived from the first growing-point of the seedling. But this 

 is a direct remnant of the substance of the fertiHsed oosphere, or of what I term 

 embryonic substance. The question is, then, whether the embryonic substance of the 

 oosphere itself also carries on this continuity, and this question must be answered 

 decidedly in the affirmative : the numerous careful embryological researches of 

 the last forty years leave no doubt that the oospheres as well as zoosperms and 

 pollen-grains arise from mother-cells which are direct descendants of growing- 

 points, from which the more elaborate sexual organs which give rise to them 

 proceed ; Goebel's recent investigations especially show emphatically that al- 

 ready in the earliest stages, the cells from which the proper sexual cells are lo 



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