162 Plant Life and Evolution 



it is not impossible that from this primitive group 

 more than one line leading to the other may have 

 arisen. 



Recent Theories as to Origin of Angiosperms 



Several recent writers have argued for the deriva- 

 tion of all the angiosperms from types allied to 

 some of the Mesozoic Cycadales, in which the sporo- 

 phylls are arranged very much as they are in the 

 living magnolia. It is also argued that the gym- 

 nosperms and pteridophytes show, for the most 

 part, structures approximating the dicotyledonous 

 type, rather than that of the monocotyledons, and, 

 moreover, that the embryo in the gymnosperms is 

 usually dicotyledonous. From this hypothetical 

 dicotyledonous ancestral form, with presumably 

 woody stem and amphisporangiate flowers, types 

 with the simpler monosporangiate flowers, and 

 herbaceous habit, would be derived by reduction. 



There may, however, be said, on the other side, 

 that most of the gymnosperms and pteridosperms 

 are monosporangiate, and primitively so. More- 

 over, the embryo of the ferns, and the same is true 

 of the peculiar aquatic heterosporous pteridophyte 

 Isoetes, which in many ways is strikingly similar in 

 habit to the monocotyledons, is monocotyledonous ; 

 so it will be seen that something may be said for the 

 assumption that the primitive angiosperms were 

 monocotyledons and monosporangiate. It seems to 

 the writer that the evidence available indicates that 

 the two types of flower the monosporangiate type, 



