PROBLEMS OF MODERN SCIENCE 



From a consideration of all these forms, Arber 

 concludes that there were three separate lines of 

 evolution from thallophytic Algas to cormophytic 

 land-plants : (i) The Sphenopsida, derived from 

 Algas with branches in whorls and leading to such 

 fossil forms as Sphenophyllum ; (2) Pteropsida, 

 from Algas with large and numerous scattered 

 branches, leading to the ferns and their descendants; 

 and (3) Lycopsida, from Algas with aerial axes 

 rarely branched, but sometimes dichotomous, lead- 

 ing to the modern Lycopods and their allies. In 

 this way a subject of fundamental theoretical in- 

 terest, which was until very recently supposed to 

 be a field only for speculation, has now become a 

 matter of direct investigation, and we have before 

 us for the first time the possibility of learning 

 something of the actual steps by which plants 

 emerged from the water and began their conquest 

 of the land. The evidence at any rate, as Dr 

 Scott says, " clearly supports the hypothesis that 

 land-plants arose from highly organised Algas of 

 the sea," and that land-vegetation therefore is not 

 descended from primitive terrestrial types, but 

 from highly developed marine types, in general 

 agreement with the views of Church. 



Ecology 



Another branch of botany which may be said 

 to have taken its rise about the end of the last 

 160 



