358 



XXVI. REPRODUCTION OF THE PTERIDOPHYTA. 



of polygonal cells, containing numerous chlorophyll bodies. In 

 the anterior indentation lies the small-celled meristem of the 

 growing point, Only in its central portion is the prothallium 

 multilamellar, as can readily be proved by changing the focus. 

 This median portion is the so-called cushion. It passes over at 

 the sides into the unilamellar portion, and slopes gradually also 

 towards the base of the prothallium. From the hinder parts of the 

 prothallium, i.e., those farthest from the growing apex, arise 

 the rhizoids ; they are especially produced in the median line of 

 the prothallium. They are long unicellular sacs, which soon 

 become brown. At the edge and under side of the prothallium, 

 individual cells, moreover, grow out into short, almost invariably 



unicellular, papillae, which, like the 

 rhizoids, are cut off by a partition 

 wall at their base. 



The Antheridia. If we have 

 chosen for examination compara- 

 tively young prothallia, they are 

 male ; if we have taken those which 

 are too old, they bear exclusively 

 female sexual organs. Intermediate 

 are such as bear both sexual organs. 

 The sexual organs, like the root- 

 hairs, stand only on the ventral 

 side of the prothallium. The male 

 sexual organs, Antheridia, are 

 found on the hinder parts of the 

 prothallium ; they arise between 

 the root-hairs ; but also beyond these on the flanks of the cushion. 

 Their formation proceeds acropetally. They appear as spherical 

 arched structures (Fig. 131, A), which, in a ripe condition, con- 

 tain smaller, globular cells in great number inside a unilamellar 

 wall. Farther behind the ripe antheridia stand those which are 

 already emptied, recognisable by the browning of their inner 

 walls, and a stellate gap in their lid-cell. A full insight into the 

 structure of the antheridia is only obtained when we examine 

 them in profile. Such profile views are not seldom obtained 

 in many accidentally- bent parts of the prothallium ; we obtain 

 them easily, also, if we fold suitably with needles prothallia 

 which are rich in antheridia. In correct profile views (Fig. 131, 

 A) we can now readily determine that the antheridium is seated 



FIG. 131. Potyvpdium inilgare. A , 

 ripe ; B, emptied antheridium ; p, 

 cell of the prothallus ; 1 and 2, lateral 

 cells ; 3, lid or cover cell. A and B 

 (x 240). (7, a spermatozoid in move- 

 ment ; D, one fixed with iodine solu- 

 tion. C and Z>(x 540). 



