PROCEEDINGS 



OF THE 



WASHINGTON ACADEMY OF SCIENCES 



Vol. IX, pp. 159-17S. July 31, 1907. 



ORIGIN AND EVOLUTION OF ANGIOSPERMS 

 THROUGH APOSPORY. 



By O. F. Cook. 



The phylogeny of the coniferous plants or gymnosperms has 

 been traced through the ferns and the Cycadofilices, an extinct 

 intermediate group. Evidence of this alliance of the gymno- 

 sperms has increased rapidly in recent years, but has not been 

 accompanied by any equally convincing indications that the 

 angiosperms or true seed-bearing plants shared the same pteri- 

 dophytic ancestry. Morphologists may be willing, therefore, 

 to consider an alternative possibility, that the origin of the 

 angiosperms should be sought more directly in some such prim- 

 itive condition as the thallose liverworts, without the need of 

 following back through the stages of development represented 

 by the ferns and other " vascular cryptogams." 



This briefer course of evolution would be opened if we were to 

 consider the female reproductive apparatus of the angiosperms 

 as analogous to the fern-prothallia which are sometimes pro- 

 duced directly from the parent plant, without the intervention 

 of spores, that is, by aposporous growth from cells of the 

 parent fronds. In this method of development the aposporous 

 prothallus serves as means of attachment for the young plant 

 during its embryonic stages, and can supply it with food- 

 materials drawn from the parent. 



A reason why this rather obvious analogy has failed to receive 

 adequate consideration in the past may be found in the fact that 

 apospory is usually associated with apogamy or other absence 

 of normal fertilization, and is commonly thought of as a method 



Proc. Wash. Acad. Sci., July, 1907. 159 



