6/8 MICROSCOPIC STRUCTURE OF HIGHER CRYPTOGAMS 



A 



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, ) ; 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 110 

 f(A\t/ = V>.i 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 aiitherids and an the- formation into a large 

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

 of the cells of the prothallium showing the anthe- the a ntherozoid-wot/,, r 

 ridial cell b, with its sperm-cells e, within the cavity 77 / \ i f f 1 



of the original cell a. B, antherid completely ce ^ (C) ; each Ot 

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

 cells, each enclosing an antherozoid. C, anthero- fQvp. c 





irv (- .,4- fi v o4- 



.-. 1-11 r* i i j_ i i-VJllJ. vvllo. 11L/U <LU J.-I- J. Q I 



zoid move highly magnified, showing its liM'ge ex- . , , ' . . ,, ,. 



tremity a, its small extremity b, and its cilia d, d. provit lei I 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 sj term- 

 cells themselves burst. 

 and give exit to their 

 antherozoids (C), which 

 execute rapid move 



inents of rotation on 

 FIG. o22. Archegone of Pteris serrulata : A, as , 



seen from above ; , a, a, cells surrounding the tnei 



base of the cavity; 1>, c, </, successive layers of pendent on the 



cells, the highest enclosing a quadrangular orifice. c .j}J.j with which 



B, side view, showing A, A, cavity containing the . , , 



germ-cell, ; B, B, walls of the archegone, made al>e lurnisneu. 



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



an opening,/, on the summit; c, c, antherozoids f pwpv mlipv ml 



1 1 IT i i . -t -i ..-i J.C W C J. Ill lllllll''vTI, CI/JU1VI 



within the cavity; </, large extremity; li, vibratile f , ,... 



cilia; z, small extremity in contact with the germ- are tOUnd upon a dll- 

 cell, and dilated. ferent part of the pro- 



thallium. Each of them 



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

 -nlidivision by a hori/ontal partition. Of the two cells thus produced 

 the upper gi \cs origin, by successive subdivisions, to the 'neck' of 

 the archegone, which, \\hen 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 cliininev or shaft. ' II ie lower of the 

 t\vo first-formed cells becomes the central cell of the archeyone : 



axes, j tartly de 

 long 

 they 



