678 MICROSCOPIC STKUCTUEE OF HIGHER CRYPTOGAMS 



especially in the neighbourhood of the rhizoids. Each has its origin 

 in a peculiar protrusion that takes place from one of the cells of the 

 prothallium (fig. 521, A, a); this is at first entirely filled with 

 chlorophyll-granules, but soon cell-division sets up in it. A central 

 cell b becomes distinguished from all the rest by its much larger size 



and is surrounded by one 

 or two layers of much 

 smaller cells known as 

 the tapetal or mantle- 

 cells. These take no 

 part in the formation of 

 the antherozoids ; but 

 the protoplasmic con- 

 tents of the large central 

 cell divide by free-cell- 



FIG. 521. Development of the antherids and anthe- formation into a large 

 rozoids of Pteris serrulata: A, projection of one number of cells known as 

 of the cells of the prothallium, showing the anthe- f^e anther ozoid-wwther- 

 ridial cell b, with its sperm-cells e, within the cavity // / \ i f -i 



of the original cell a. B, antherid completely ^ (c) ; each ot these 

 developed ; a, wall of antheridial cell ; e, sperm- again breaks up into 

 cells, each enclosing an antherozpid. Canthero- four cellg not at first 

 zoid more highly magnified, showing its l*rge ex- . , , '., , ,, ,, 



tremity a, its small extremity b, and its cilia d, d. provided with cell-walls, 



the sperm-cells. Each 

 of the sperm-cells (B, e) 

 is seen, as it approaches 

 maturity, to contain a 

 spirally coiled filament ; 

 and when set free by 

 the bursting of the 

 antherid the sperm- 

 cells themselves burst, 

 and give exit to their 

 antherozoids (C), which 

 execute rapid move- 



ments of rotation on 

 FIG. 522. Archegone of Pteris serrulata : A, as ,. , , 



seen from above; a, a, a, cells surrounding the their axes, partly de- 

 base of the cavity ; b, c, d, successive layers of pendent on the long- 

 cells, the highest enclosing a quadrangular orifice. c ^j a w fth which they 

 B, side view, showing A, A, cavity containing the '11 



germ-cell, a ; B, B, walls of the archegone, made are 



up of the four layers of cells, b, c, d, e, and having The archegones are 



an opening,/, on the summit; c, c, antherozoids f ewer in num ber, and 

 within the cavity; g, large extremity; h, vibratile , -,.,. 



cilia; i, small extremity in contact with the germ- are found upon a dlt- 

 cell, and dilated. ferent part of the pro- 



thallium . Each of them 



originates in a single cell of its superficial layer, which undergoes 

 subdivision by a horizontal partition. Of the two cells thus produced 

 the upper gives origin, by successive subdivisions, to the * neck ' of 

 the archegone, which, when fully developed (fig. 522), is composed 

 of twelve or more cells, built up in layers of four cells each, one upon 

 another, so as to form a kind of chimney or shaft. The lower of the 

 two first- formed cells becomes the central cell of the archegone ; 



