362 SCIENCE PROGRESS. 



ing fertilisation ; an increased number of new individuals 

 being thus produced, while the dryness of the spores when 

 ripe, which is a common character of the large majority 

 of the Archegoniatae, would facilitate their spread by 

 winds and other agencies. In homosporous forms the 

 spread and survival of the species is secured by production 

 of numerous small spores, rather than by any special 

 development or sexual differentiation of the spores them- 

 selves. 



But the larger the number of spores produced, the 

 greater will be the demand for nutrition by the parent. 

 This demand we see in part met by the adaptation of the 

 parent sexual plant to the conditions of land-life : the Mar- 

 chantiea± show this in the elaboration of structure of the 

 thallus which still maintains its simple outline, and it is 

 most interesting to note how, by a perfectly distinct mode 

 of development, a condition is attained in the highest of 

 them (Marchantia, etc.) which is not unlike that of the 

 leaves of some angiospermic plants. In other cases elabora- 

 tion of outward form takes place, as in the Jungermanni- 

 aceoe and in the true Mosses (Musci) ; these sometimes 

 simulating in a curious way the forms of the sporophyte in 

 higher types. 



But though the sexual plant might thus become elaborated 

 to subserve more liberal nutrition, this could not suffice 

 altogether, even in cases where a number of female organs 

 had been fertilised on the same individual. An increase of 

 number of spores produced from a single sporogonium necessi- 

 tates increased facility of conveyance of their nutrition to them 

 during development, and of their dispersion when mature; and 

 in the undoubtedlv ascending series of the Liverworts we 

 see most beautifully shown the advance of complexity of 

 the fruit body (sporogonium) to meet these needs ; in 

 Professor Campbell's book, pp. 2 1 -15 1, readers will rind 

 the facts collected and arranged so as to illustrate the 

 progression from simpler to more complex types of the 

 sporophyte in these plants. There is good reason to believe, 

 as the result of comparison, that there has been a process of 

 sterilisation at work, converting cells which were potentially 



