COULTER— INHERITANCE THROUGH SPORES. 345 



Furthermore, the origin of embryos produced in seeds is not 

 assured. \Miile we may assume that, for the most part, they are 

 the result of fertilization, which in its gross aspects can be controlled, 

 the increasing number of cases of parthenogenesis, vegetative 

 apogamy, and sporophytic budding introduces a serious element of 

 uncertainty. The program between pollination and fertilization, 

 and between fertilization and the escape of the embryo from the 

 seed, is a very long one, and not a single stage of it is under observa- 

 tion, much less under control. In other words, we are working 

 empirically upon our problem as yet. 



If sexual reproduction must be studied, it would seem desirable, 

 therefore, to use material selected from the more primitive sexual 

 forms, material in which the sexual structures are not so involved 

 with other structures, in which the whole performance of fertiliza- 

 tion and embryo development is in sight and capable of control. 

 The difference between a sex act and an embryo development under 

 cover, and in the open, when experimental control is the end in 

 view, is too obvious to need further explanation. Furthermore, in 

 these simpler sexual forms the origin of sex is observable, so far 

 as it is represented by the sexual cells, and the general conditions 

 of origin are known, conditions which are sadly in need of analysis 

 in experimental work. It must be evident that a knowledge of 

 the factors involved in the origin of sex may throw some light on 

 the function of sex in general. But the origin of sex involves a 

 still more fundamental problem. 



Sexual cells are phylogenetically related to spores, that is, spores 

 are historically intermediates between vegetative protoplasts and 

 sexual cells. This suggests that the origin of spores and in- 

 heritance through them deserve attention as a preliminary to the 

 origin of sexual cells and inheritance through them. In other 

 words, there are certain things that all forms of reproduction have 

 in common, and these should be kept distinct from the things which 

 are peculiar to sexual inheritance. 



yiore primitive than reproduction by spores is reproduction by 

 ordinary protoplasts, shown notably by one-celled plants in which 

 cell division results in reproduction and in which the succession of 



