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TEXTBOOK OF BOTANY 



Fig. 329. Longitudinal section of a part of an ovule of a cycad (Diodn) at time 

 of fertilization. The reproducti\e structures represented are the pollen tubes in 

 the nucellus; the spirally ciliated sperms: and two archegonia. one (right) with 

 egg, the other (left) after union of sperm and egg nucleus. Surrounding the 

 archegonia is the female prothallus. Drawing by C. J. Chamberlain. 



the driest deserts. The vegetation of prairies, plains, deserts, most tropi- 

 cal forests, and the deciduous forests is dominated by angiosperms. 

 Furthermore, the undergrowth of most conifer forests contains flower- 

 ing plants. Our most valuable crop and forage plants and our most 

 annoying weeds are angiosperms. 



The seeds of angiosperms are enclosed in ovularies. Variously colored 

 bracts and floral lea\'es appear in whorls around the spore-bearing 



