386 VASCULAR CRYPTOGAMS. 



often produced on the same prothallium. In the Rhizocarpeae, Selaginelleaj, and 

 Isoeteaj, on the other hand, the separation of the sexes is already prefigured by the 

 two kinds of spores, the Macrospores being female, in so far as they develope 

 a small prothallium, which produces exclusively archegonia, or sometimes only 

 a single one ; the Microspores being male, inasmuch as they develope a still smaller 

 prothallium bearing exclusively antheridia. The female prothallium of the Rhizo- 

 carpeae is a small appendage of the macrospore, formed in its interior but afterwards 

 developed externally although nourished by it; in Selaginelleae and Isoeteae the 

 prothallium is developed in the spore itself, filling it up with a mass of tissue, the 

 archegonia becoming exposed only by the splitting of the cell-wall of the spore. 

 The male prothallium consists, in these groups of plants, of a single sterile or 

 vegetative cell, and of a larger or smaller number of cells in which antherozoids 

 are developed. 



The Archegonia of Vascular Cryptogams, like those of the Muscineae, are 

 bodies, consisting of a ventral part which encloses the oosphere, and of a neck, 

 usually short and composed of four longitudinal rows of cells. The two groups 

 differ in the fact that in Vascular Cryptogams the tissue of the wall of the ventral 

 part is formed from the prothallium itself; and the ventral part of the archegonium 

 is therefore enclosed in the tissue of the sexual generation, the neck only projecting 

 beyond it. The archegonium originates from a superficial cell of the prothallium 

 which is divided by a tangential wall into two, an external and an internal. The 

 former forms, by intersecting longitudinal and subsequent transverse divisions, the 

 four rows of cells of the rather short neck ; the latter grows outwards between the 

 neck-cells into a projection which becomes separated, forming the neck-cell, and 

 another segment is cut off from the large inferior cell (the central cell, Janczewski) 

 to form the ventral canal-cell. Thus there arises from the original internal cell an 

 axial row of three cells, the lowest of which is the oosphere. The two neck-cells 

 become converted into mucilage as in the Muscineae. The mucilage thus produced 

 in the neck finally swells up considerably, forces apart the four apical cells of the* 

 neck, and is expelled ; an open canal is thus formed, leading from without to the 

 oosphere ; the expelled mucilage appears to play an important part in the conduc- 

 tion of the ' swarming' antherozoids to the opening of the neck. Fertilisation is 

 always effected by means of water, which determines the opening of the antheridia 

 and archegonia, and serves as a vehicle for the antherozoids. The advance of these 

 latter as far as the oosphere, and even their entrance into and coalescence with its 

 protoplasm, has been directly observed in the different groups. 



The Antherozoids^ are, like those of the Muscineae, spirally coiled threads usually 

 with a number of fine cilia on the anterior coils. In the cases hitherto observed they 

 arise from the peripheral part of the protoplasm of their small mother-cells, a central 

 vesicle of protoplasm, containing starch-grains, being left over, which, adhering to a 

 posterior coil of the antherozoid, is often dragged along by it, but is detached before 



^ [On the development of the antherozoids of the Vascular Cryptogams, see Strasburger, Zell- 

 bildung und Zelltheilung, 3rd, ed. 1880, The formation of the antherozoid is, in all cases, preceded 

 by the disappearance of the nucleus of the mother-cell, its substance becoming diffused throughout 

 the protoplasm.] 



