MERISTIC PHENOMENA 33 



readily distinguishable. There is the event by which the cell 

 divides, and the event by which the two halves or their descend- 

 ants are or may be differentiated. It is common knowledge that 

 in some cell-divisions two similar halves, indistinguishable in 

 appearance, properties, and subsequent fate, may be produced, 

 while in other divisions daughter-cells with distinct properties 

 and powers are formed. We cannot imagine but that in the 

 first case, when the resulting cells are identical, the division 

 is a mechanical process by which the mother-cell is simply 

 cut in two; while in order that two differentiated halves may be 

 produced, some event must have taken place by which a chemical 

 distinction between the two halves is effected. 1 In any ordinary 

 Mendelian case we have a clear proof that such a chemical dif- 

 ference may be established between germ-cells. The facts of 

 colour-inheritance for instance prove that germ-cells, otherwise 

 identical, may be formed possessing the chromogen-f actor which 

 is necessary to the formation of colour in the flowers, or destitute 

 of that factor. Similarly the germ-cells may possess the ferment 

 which, by its action on the chromogenic substance, produces 

 the colour, or they may be without that ferment. The same 

 line of argument applies to a great range of cases. Nevertheless, 

 though differences in chemical properties are often thus consti- 

 tuted by cell-divisions, and though we are thus able to make a 

 quasi-chemical analysis of the individual by determining and 

 enumerating these properties, yet it is evident that the dis- 

 tribution of these factors is not itself a chemical process. This 

 is proved by the fact that similar divisions may be effected be- 

 tween halves which are exactly alike, and also by the fact that 

 the numbers in which the various types of germ-cells are formed 

 negative any suggestion of valency between them. The recog- 

 nition of the unit-factors may lead — indeed must lead — to great 

 advances in chemical physiology which without that clue would 

 have been impossible, but in causation the chemical phenomena 

 of heredity must be regarded as secondary to the physical or 



1 In saying this we make no assumption as to the particular cell-division at 

 which differentiation occurs. This may be one of the maturation-divisions, or it 

 may perhaps be much earlier. 



