THE VITAL PROPERTIES OF THE CELL 305 



similar to that performed by the mucoid and gelatinous envelopes 

 of many ova which retain the antherozoids. 



On the other hand, they in no wise explain conjugation itself, 

 i.e. the processes peculiar to fertilisation. This may be proved in 

 a very simple manner. According to the researches of Pfeffer, 

 malic acid is secreted in the archegonia of the most different Ferns. 

 Nevertheless, only the antherozoids of the same species will fuse 

 with the oosphere, those of a different species being as a rule un- 

 able to fertilise them. Thus we see, that there are relations exist- 

 ing between the sexual products which cannot be explained by 

 the action of irritating chemical secretions. The same is true of the 

 conjugation of gametes, of the formation of the receptive promin- 

 ence in animal ova, and of the mutual attraction of egg- and 

 sperm-nuclei. 



Nageli (IX. 20) suggests that electrical forces may be the cause 

 of sexual attraction, and this seems to me to be an explanation 

 of far-reaching importance. But, until this conjecture has been 

 definitely proved, it is better to attribute the sexual phenomena in 

 general to the reciprocal action of two somewhat differently 

 organised protoplasmic bodies, and to call this reciprocal action 

 sexual affinity. We must be content with such a general ex- 

 pression, since we cannot accurately analyse the forces which come 

 into activity. Presumably it is not a question here of a simple 

 phenomenon, but of a very complicated one. 



This may be rendered still clearer by an investigation of the 

 second point, namely, what is the nature of the cells requiring 

 fertilisation, and between which there is sexual affinity ? 



b. More minute discussion of sexual affinity, and its 

 different gradations. The possibility of the occurrence of 

 fertilisation, and the results produced by it, are to a great extent 

 determined by the degree of relationship which exists between the 

 sexual cells. But since a near relationship implies a greater or 

 less similarity in their organisation, these differences in their 

 organisation must be the determining factor. 



The degree of relationship between the two cells may vary con- 

 siderably. It is nearest when both the cells to be fertilised are 

 descended directly from the same mother cell; it is more distant 

 where many cell-generations have developed asexually from the 

 mother-cell, the final products at last producing sexual cells. 

 Here, too, cases of nearer or more distant relationship are possible. 

 If we take as an example one of the higher flowering plants, we 



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