SEXUAL REPRODUCTION. 



289 



sexual spores arise (fig. 330), which produce the gametophyte 

 again. 



390. A compound ovary consists of a central row of cells 

 (each of which is homologous with a simple ovary) surrounded 



Fig. 330. — A, a bit of a red seaweed bearing a mature cystocarp ; seen from the side. 

 The spores show through the translucent wail. B, a diagram of a section through the 

 same, showing spores as enlarged terminal cells of twigs arising from a basal cell of the 

 cystocarp. The shaded parts arise from the fertilized egg (= a sporophyte), the case 

 developing by induced growth. Magnified 25 diam. — After Falkenberg. 



by a wall composed of one or more layers of cells. Of the 

 central cells only the lowest produces an egg. The upper 

 ones break down into mucilage, by the swelling of which the 

 ovary is opened, and by its escape in whole or part a canal is 

 formed leading to the egg (fig. 332). Down this canal the 

 sperms make their way, and one fertilizes the egg. 



The compound ovary is known as an archegonium. When 

 best developed, it is a flask -shaped structure (fig. 331) con- 

 sisting of a body and a neck. In the body is the cell con- 

 taining the egg. Compound ovaries may be stalked, sessile, 

 or sunk in the tissues of the gametophyte. They are found 

 only in mossworts, fernworts, and seed plants. In the latter, 

 however, they are simplified out of all likeness to the form 

 described. 



391. Mossworts.— When the gametophyte is differentiated 

 into stem and leaves, as in mossworts alone, they are formed 

 upon the stem. Usually several are developed in the same 

 neighborhood, when they are generally protected by over- 



