190 THIRD GROUP. 



prothallium which produces only archegonia and sometimes only a single one. The 

 female prothallium of the Rhizocarpae is a small appendage of the large spore ; it is 

 formed inside it, emerges from it afterwards, and is fed by it. In the Selaginelleae 

 and Isoeteae, on the contrary, the prothallium is entirely developed inside the spore, 

 which it fills with its tissue, and only the archegonia come forth to the light through 

 fissures in the outer coat of the spore. The microspores on the other hand are male, 

 their very rudimentary prothallium producing only antheridia. 



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

 bodies of cellular tissue, consisting of a venter which contains the oosphere, and a 

 neck which is usually short and formed of four longitudinal rows of cells ; there is 

 this difference between the two groups, that in the Vascular Cryptogams the tissue of 

 the wall of the venter is formed from the tissue of the prothallium itself, and the venter 

 therefore is enclosed in the tissue of the oophyte, the neck only projecting above 

 it. The archegonium originates in a superficial cell of the prothallium, which divides 

 by a tangential (periclinal) wall into an inner and an outer cell ; the latter by longi- 

 tudinal divisions which cross one another and subsequent transverse divisions produces 

 the four rows of cells of the shorter or longer neck ; a projection from the inner cell 

 pushes in between the cells of the neck (Fig. 151), and is then divided off and is the 

 neck-canal-cell, while from the larger cell below it (Janczewski's central cell) another 

 small portion is cut off to form the ventral canal-cell. In this way an axile row of 

 three cells is formed from the original inner cell, and the lowest of the three 

 forms the oosphere ; the two neck-cells are converted into mucilage as in the 

 Muscineae. The 'mucilage thus formed in the neck at length swells considerably, 

 forces open the four apical cells of the neck, and is ejected ; thus an open passage 

 is formed leading from the outside to the oosphere, and the ejected mucilage 

 appears to play an important part in the conducting of the swarming spermato- 

 zoids to the orifice of the neck. Fertilisation is in all cases brought about by the 

 agency of water, which causes the antheridia and archegonia to open, and serves 

 as a vehicle for the spermatozoids ; these have been directly observed in the different 

 classes to make their way to the oosphere and into it, and to coalesce with its proto- 

 plasm. The spermatozoids are spirally coiled threads usually with numerous delicate 

 cilia on the anterior coils; they are formed in exactly the same way as in the 

 Characeae and the Muscineae, that is, they come chiefly from the nucleus of the mother- 

 cell, which becomes thicker at its circumference and splits into the coiled thread of 

 the spermatozoid. There is left after this process a vesicle of protoplasm containing 

 starch-grains, which adheres to a posterior coil of the spermatozoid and is carried along 

 with it, but is swept off before the spermatozoid enters the archegonium. The mother- 

 cells of the spermatozoids (spermatocytes) are formed in antheridia, which are roundish 

 bodies rising free from out of the prothallium in the true Ferns and Equisetaceae, but 

 sunk in it in the Ophioglosseae, Marattiaceae and Lycopodium ; among the hetero- 

 sporous forms Salvinia has a very simple antheridium which emerges from the 

 microspore, while the Marsiliaceae and Selaginelleae produce their antheridia inside 

 the microspore, after a tissue consisting of a few cells, or of one cell only in Marsilia, 

 has been formed in it, which we must regard as a rudimentary prothallium. 



The second orSEXUAL GENERATION (sporophore, sporophyte), which produces 

 the spores, proceeds from the oospore in the archegonium. The first divisions of 



