356 MICROSCOPIC STRUCTURE OF HIGHER CRYPTOGAMIA. 



but its essential structure always remains the same. From its 

 under surface are developed, not merely the root-fibres (a, b) 

 which serve to fix it in the soil, and at the same time to supply 

 it with moisture, but also the antheridia and archegonia, which 

 constitute the true representatives of the essential parts of the 

 flower of higher Plants. Some of the antheridia may be dis- 

 tinguished at an early period of the development of the prothal- 

 lium (A, h) ; and at the time of its complete evolution these bodies 

 are seen in considerable numbers, especially about the origins of 

 the root-fibres. Each has its origin in a peculiar protrusion that 

 takes place from one of the cells of the prothallium (Fig. 146, A, a) ; 



FIG. 146. 



Development of the Antheridia and Antherozoids of Pteris serrulata: A, projection of one of the 

 cells of the prothallium, showing the antheridial cell, 6, with its sperm cells, e, within the cavity of 

 the original cell, a ; B, antheridium completely developed ; a, wall of antheridial cell ; e, sperm- 

 cells, each enclosing an antherozoid ; c, one of the antherozoids more highly magnified, showing a, 

 its large extremity, b, its small extremity, d, d, its cilia. 



this is at first entirely filled with chlorophyll-granules ; but soon 

 a peculiar free cell (b) is seen in its interior, filled with mucilage 

 and colorless granules. This cell gradually becomes filled with 

 another brood of young cells (<?), and increases considerably in its 

 dimensions, so as to fill the projection which encloses it ; this 

 part of the original cavity is now cut off from that of the cell of 

 which it was an offshoot, and the antheridium henceforth ranks 

 as a distinct and independent organ. Each of the secondary cells 

 (B) contained within its primary cell, is seen, as it approaches 

 maturity, to contain a spirally coiled filament ; and when they 

 have been set free by the bursting of the antheridium, they them- 

 selves burst and give exit to their " antherozoids" (c), which exe- 

 cute rapid movements of rotation on their axes, partly dependent 

 on the six long cilia with which they are furnished. The arche- 

 gonia are fewer in number, and are found upon a different part 

 of the prothallium. Each of them at its origin presents itself 

 only as a slight elevation of the cellular layer of the prothallium, 

 within which is a large intercellular space containing a peculiar 

 cell (the "germ-cell"), and opening externally by an orifice at 

 the summit of the projection ; but when fully developed (Fig. 147), 

 it is composed of from ten to twelve cells built up in layers of 

 four cells each, one upon another, so as to form a kind of chim- 

 ney or shaft, having a central passage that leads down to the 

 cavity at its base, wherein the germ-cell is contained. Into this 

 cavity the antherozoids penetrate, so as to come into contact with 



