274 CONCLUDING CHAPTER 



gametes, as well as to the mass of cells to which the 

 zygote (in the strictest sense) eventually gives rise. 

 In the simplest forms, such as the algae, the cell- and 

 nuclear-fusion constituting conjugation are imme- 

 diately followed by fusion of the chromosomes, an 

 event which we have seen to be the first step towards 

 a reduction in the number of these bodies. In the 

 higher plants, by delaying this fusion of chromosomes 

 until many cell generations later than the fusion of the 

 nuclei, the advantages associated with the possession 

 of a double nucleus have been obtained for a large and 

 complicated mass of cells. And this mass has gradu- 

 ally advanced in organization and relative importance, 

 until ultimately the ^-generation has been reduced 

 almost to the vanishing point. 



The sex-phenomena of the higher animals can most 

 readily be brought into line with those of the higher 

 plants if we consider that in animals the spore and the 

 gamete are identical ; the ^-generation is here con- 

 densed into the smallest possible limits namely, those 

 of a single cell. 



A female animal produces ova, and a male produces 

 spermatozoa. Similarly, we may regard as a female 

 plant one which produces only the larger variety of 

 spores from which ova arise ; and we may regard as a 

 male plant one which produces only pollen. It is 

 much more usual to find a flowering plant bearing both 

 pistils and stamens, and producing both large and small 

 spores. Such an organism is described as herma- 

 phrodite bearing both sexes. Among animals ex- 

 amples of hermaphrodite species are also not infrequent, 



