FIL1CINEAE. HOMOSPOROUS FILICINEAE. 203 



colourless granules, which afterwards drops off and lies where it falls, while the thread 

 hastens away by itself. The spermatozoid in the Ferns, as in the Muscineae, 

 according to the latter researches of Schmitz and others, is derived almost entirely 

 from the nucleus of the mother-cell, the cilia perhaps being formed from the pro- 

 toplasm. The nucleus becomes thickened at its circumference, and of looser con- 

 sistence towards its centre ; the body of the spermatozoid is produced by the splitting 

 up of the periphery, the central part supplying the vesicle, which is thus not 

 properly a part of the spermatozoid but only clings to it and swells up strongly by 

 endosmose in water, as Fig. 1 50 shows. 



The archegonium proceeds from a superficial cell of the prothallium, which first 

 arches slightly outwards, and is divided into three cells by two walls parallel to the 

 upper surface ; the lowest of these, called by Janczewski the basal cell, (Fig. 151 A, e\ 

 subsequently divides in the same way as the cells of the surrounding tissue, and thus 

 contributes to the construction of the venter of the archegonium which is entirely 

 sunk in the thallus. The outermost of the three primary cells produces the wall or 

 periphery of the neck of the archegonium (Fig. 151 A, h h) by first dividing cross-wise 

 into four cells, from which the four rows of cells forming the wall of the neck are 

 derived by the formation of obliquely transverse walls ; as the neck grows faster and 

 becomes convex on the anterior side, that is on the side towards the apex of the 

 prothallium, the number of the cells in the front rows of the neck is larger, usually 

 six, while that of the cells on the shorter concave posterior side of the neck is usually 

 four. The middle of the three primary cells produces the central cell and the neck- 

 canal-cells, that is, the entire axile row of cells in the archegonium ; during the 

 formation of the periphery of the neck this middle cell becomes pointed at its upper 

 end and forces itself in between the cells of the neck (Fig. 151 A); the pointed end 

 is cut off by a transverse wall and now forms the single neck-canal-cell (Fig. 151 A, k), 

 which elongates as the neck grows longer, completely fills it, and according to Stras- 

 burger shows a tendency to further transverse divisions by the appearance of a few 

 nuclei, but does not form any septa (Fig. 151 B\ though Janczewski doubts this 1 . 

 The broad central cell now divides into an upper smaller cell, the ventral canal-cell 

 (Fig. 152 B s), and into the much larger oosphere (<?) which is subsequently rounded 

 off. The walls of the canal-cells swell and are converted into mucilage, and the watery 

 mucilage together with the protoplasm of the canal-cells is at length expelled through 

 the opened neck. The spermatozoids collect in great numbers and are caught in the 

 mucilage in front of the archegonium ; many make their way into the canal and often 

 stop it up ; single ones reach the oosphere, enter it and disappear in it ; they enter 

 at a clearer spot in the oosphere towards the neck, which is termed the receptive spot. 

 (See the oogonia of the Algae 2 ). 



The second or asexual generation (sporophore^ sporophyte), the Fern, is the pro- 

 duct of the oospore formed by fertilisation of the oosphere in an archegonium. The 

 surrounding tissue of the prothallium at first keeps pace with the increase in size 

 of the embryo, which remains for some time enclosed in a projection from the 

 under surface of the prothallium, till the first leaf and the first root burst from it. 



1 He is wrong here. Compare Marattia. 



2 Strasburger says that the act of fertilisation may be observed with unusual distinctness in 

 Ceratopteris. Hofmeister long ago saw the spermatozoids penetrate to the oosphere. 



