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MORPHOLOGY 



at least it secures the development of male and female gametophytes 

 in close proximity. 



Gametophyte. — The gametophyte is a small, green, branching rib- 

 bon, being strictly a thallus, without any of the subterranean develop- 

 ment that characterizes Lycopod'mm. Although the gametophytes are 

 usually dioecious, and the female gametophytes are larger and more 

 massive than the male (figs. 343, 344), the spores are all approximately 

 the same size. Certain of the ancient representatives of the Equise- 

 tales, however, have been found to be heterosporous. 



Antheridium. — The antheridium is interesting in that it shows two 

 kinds of development, dependent upon its position. If it occurs in the 



axial region of the thallus, it 

 develops as usual among euspo- 

 rangiates; that is, a superficial 

 initial cell is divided by a pen- 

 cil rial wall, the outer cell pro- 

 ducing the wall of the anther- 

 idium, the inner cell producing 

 the spermatogenous tissue (figs. 

 345, 347, 348). If it develops 

 in a terminal position on the 

 thallus, the superficial initial 

 cell forms first a papillate out- 

 growth, which is cut off by a 

 periclinal wall, and it is this 

 protruding cell that develops 

 the antheridium (fig. 346). In 

 this cell an apical cell with 

 three cutting faces is formed, 

 and then a domelike cap cell 

 is cut off, leaving a central cell, 

 which produces the spermatoge- 

 nous tissue, invested by four 

 peripheral cells, which develop the wall of the antheridium. This 

 type of antheridium development is characteristic of certain modern 

 ferns. The sperms are very large, spirally coiled, and multiciliate 



(fig- 349). 



Archegonium. — The archegonium always develops from the massive 

 axial region and in the axil of a branch. It develops as among other 



FlGS. 345-349. — Antheridium of Equisetum : 

 345, one type of development, showing the peri- 

 clinal division, the inner cell being spermatog- 

 enous ; 346, the other type of development, 

 showing the papillate protruding cell (peri- 

 clinal wall below), in which are shown two 

 segments (the third behind) cut off by the 

 apical cell, the dome or cap cell, and the en- 

 closed spermatogenous cell; 347, 348, nearly 

 mature antheridia of the first type; 349, a 

 sperm. — 345-348, after Goebel; 349, after 

 Belajeff. 



PROPERTY OF 



»*E COLLEGE Ui 



