CONCLUSION 225 



no nearer together; the plant remains a plant 

 and the fruit a fruit, as before. 



If, then, the theory that the asexual plant of 

 the higher Cryptogams was derived from a 

 sporogonium is unsupported by evidence, what 

 other theory is tenable? Obviously, the simple 

 one that the vegetative plant has always been a 

 vegetative plant that the Fern with its stem 

 and leaves corresponds to the Seaweed, in which 

 stem and leaf are not yet differentiated, the 

 whole plant being a thalltis. On this view, the 

 life-history which we now find in the Ferns con- 

 sists essentially in the regular alternation of an 

 individual bearing sexual organs and an indi- 

 vidual bearing sporangia, the two individuals 

 having been equivalent to start with, though 

 one has come to be more highly developed than 

 the other. There are excellent analogies for this 

 among the Seaweeds, especially in Dictyota, a 

 brown Alga, common on our coasts, with a forked, 

 strap-shaped thallus. Here there are sexual 

 organs and asexual spores, always borne on dif- 

 ferent plants. The sexual and asexual individuals 

 alternate regularly. The fertilised egg-cell grows 

 up into a spore-bearing plant, and when the 

 spores of the latter germinate they produce the 

 sexual plant again, and so on. The alternation 

 is just as regular as in the Fern, but the sexual 

 and asexual individuals are exactly alike. There 



