GAMETOPHYTE. 35 



Meanwhile many rhizoids are reaching- from the under surface of the 

 prothallus into the earth (fig-. 231). Hitherto all of the divisions men- 

 tioned have been vertical, and there is but one layer of cells. When, as 

 in female plants, a "cushion" is formed in the middle of the prothallus, 

 divisions parallel to the surface occur in the posterior segments of the 

 initials (figs. 202, 205-207, 214). The upper half of the segment may 

 divide once or twice in this plane, giving- rise to two or three layers of 

 cells. The lower half is responsible for most of the bulk of the cushion 

 and for all of the organs which appear thereon (figs. 206, 207). In 

 crowded cultures wart-like outgrowths occur on the upper surface of the 

 prothallus (fig. 201). They can only be considered as abnormalities. 



The prothallia reach sexual maturity at five weeks and later from sowing 

 of spores. They are practically always dioecious. Only three hermaph- 

 rodites have I seen. On one of these male and female organs seemed to 

 be mature at the same time. The males mature first, and they may con- 

 tinue to grow and bear great numbers of antheridia for five months or 

 more. Antheridia may appear on very small plants. I found one in a glen 

 near Baltimore, Maryland, in which there were four prothallial cells and 

 three antheridia (fig. 198). All sizes and shapes occur from this up to 

 those which are 5 mm. across, with many lobes, and the margins crisped like 

 a "curly" lettuce-leaf. Whether those which bear sexual organs at a very 

 early age ever develop to large size I do not know. Probably they do not. 



The male prothallus is always but one cell thick; it has no cushion. 

 The antheridia arise at any point on the shaded side central or marginal 

 (figs. 227, 228). In large "curly" specimens the relation to light is 

 clearly shown. A section may show an S-shaped portion of prothallus. 

 Supposing the light to come from the upper edge of the page, the anthe- 

 ridia will be found on the lower side of each transverse bar of the S. 

 Two of these will be the morphologically lower surface and one the upper. 

 At transition points two antheridia may be seen on opposite sides of the 

 same cell ! 



The antheridium arises from the prothallial cell as a papilla, which is 

 soon cut off by a basal wall (fig. 225). It differs in appearance from a 

 young rhizoid in having many chloroplasts, though the rhizoid rudiment 

 may have two or three. In preserved material this difference is not evi- 

 dent. The papilla enlarges and is cut in two by another wall parallel to 

 the first (fig. 226). The first cell is the stalk-cell, and undergoes no 

 further division; the other is the antheridial mother-cell. The next two 

 walls are those commonly described for fern antheridia, viz, first a dome- 

 shaped wall parallel to the outer wall of the mother-cell (figs. 228, 232); 

 second, a circular wall at the summit of the outer cell to form the lid. 

 The body of the antheridium now consists of a cylindrical wall-cell, a cir- 

 cular cap-cell, and a large, dense central cell. The central cell is devoid 

 of chlorophyll. It divides at first vertically (fig. 227), then in three 



