402 PART III. THE CLASSIFICATION OF PLANTS. 



Gleicheniacese generally) there is a well-developed cushion, 

 situated anteriorly in the middle line, whilst in the Schizseaceee 

 it is on one side ; in the Osmundacese the receptacle is in the form 

 of a midrib, projecting on the under surface, bearing a longitudinal 

 series of archegonia on each flank. In other cases there is a 

 definite archegoniophore, that is, the receptacle is borne on a stalk 

 which is a ventral branch of the prothallium. Thus, in Gymno- 

 gramme leptophylla (Polypodiacese), the cushion on the ventral 

 surface of the prothallium elongates into the soil and there be- 

 comes tuberous, and it is on the upper surface of this tuberous 

 archegoniophore that the archegonia are produced. Again, in 

 Aneimia (Schizseaceas), if the first-formed archegonia fail to be 

 fertilised, the cushion has been observed to grow out into an 

 archegoniophore. Finally, the flattened or massive cellular 

 appendages of the filamentous prothallium of Trichomanes incisum 

 and sinuosum may be also regarded as archegoniophores. 



The antheridia are generally borne on the posterior portion of 

 the prothallium, scattered without any definite order. It occa- 

 sionally happens that they occur in the female receptacle, or even 

 on an archegoniophore; thus, in some Hymenophyllurns, antheridia 

 have been found in the groups of archegonia, and they are frequently 

 developed on the cushion in Polypodiacese and Schizseacece ; they 

 are also developed on the flat archegoniophores of Trichomanes 

 sinuosum, and on the archegoniophore of Aneimia. 



The sexual organs. The antheridium is developed from a 

 single superficial cell. The free surface of this cell grows out into 

 a blunt protuberance, which is cut off by a transverse wall. The 

 projecting cell thus formed generally undergoes division by the 

 formation of a transverse wall near its base, so that it comes to 

 consist of two cells, the lower of which is the stalk-cell, the upper, 

 the antheridial cell. The latter grows, becoming more or less 

 spherical, and undergoes repeated cell-divisions which result in 

 the formation of a wall, consisting of a single layer of cell?, 

 surrounding a large central cell from which, by further division, 

 the mother-cells of the spermatozoids are formed. When mature, 

 absorption of water causes the rupture of the antheridium ; the 

 mother-cells of the spermatozoids are now set free, and the 

 spermatozoids soon escape from the mother-cells as coiled ciliated 

 filaments, each having usually attached to it posteriorly a vesicle 

 of granular protoplasm, the remains of the contents of the mother- 

 cell (see Fig. 266) 



