EqUISETINM. 



365 



477. — The archegonia arise upon the anterior edge of the 

 prothallium, from the division of single cells. The mother- 

 cell of the archegonium undergoes several divisions, result, 

 ing in the formation of a germ-cell, surrounded by one or 

 more layers of cells. The germ-cell lies at a considerable 

 depth beneath the general surface of the prothallium, above 



Fig. Wi.—A, fragment of a prothallium of Equisetum limosum (in the middle of 

 July) ; a, an apical cell oi a growing point ; an, a ripe antheridium, with escaping 

 sperm-cells ; afi', a young antheridium. B, longitudinal section of an archegonium 

 of Equisetum arvense immediately after the opening of its apex, showing the germ- 

 cell in the cavity below, surrounded by the parenchyma of the jirothallium. C, longi- 

 tudinal section of the germ-cell, or rudimentary embryo, of E. arvense, shortlj^ after 

 fertilization ; it is seen to be already divided into four parts, and the whole is aur- 

 rounded by the parenchyma of the prothallium. X X 200 / S and C X 300.— After 

 Hofmeister. 



■which the surrounding tissue of the archegonium is pro- 

 longed into a four-sided tube. At the period of maturity of 

 the archegonium, the projecting cells diverge from each 

 other, and form an open channel to the germ-cell {B, Fig. 

 350). 



478. — After fertilization the germ-cell undergoes division 



