OF FERNS FROM THEIR SPORES. 121 



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every condition of their development in prothallia which are fully formed. When anthe- 

 ridia appear on very young prothallia, composed of a single row of cells, or at most of a 

 double row in the upper part, they present themselves as productions from the margins, 

 the outer side of one of the cells giving origin to each cmtheridium. But as soon as the 

 prothallium has acquired anything like a flattened form, by the transverse expansion of 

 the anterior end, the antheridia are formed almost exclusively upon the inferior surface, 

 that surface in contact with the soil upon which the plant grows. They appear first upon 

 the older cells of the central region, and gradually spread forward as the prothallium 

 grows, hut appear seldom to extend beyond a certain distance from the centre, occurring 

 in greatest number about the central cushion-like protuberance above described. 



It has already been stated that they occur upon the progeny of the proliferous barren 

 prothallia ; in some cases I have found these branching at their edges and bearing anthe- 

 ridia in a very abnormal position, at the ends of projecting cellular processes (figs. 27-32); 

 this, however, afforded great facility for observing the internal structure of these organs, 

 and checking the results obtained by observations upon sections. 



The first sign of the production of an antheridium consists in the elevation of a globular 

 protuberance from the lower, free surface (or in the young prothallia from a lateral 

 surface), forming at first a kind of globular pouch (fig. 17), in which are seen at first a 

 few chlorophyll globules, which afterwards vanish and give place to a collection of light 

 yellowish, mucilaginous contents, slightly granular. A septum is soon formed, shutting 

 off this budding cell from that which gives origin to it, and as it becomes elongated 

 another cross septum often appears, a little higher up (figs. 21 & 29, &c), so that the 

 structure then consists of a basal cell forming a peduncle, as it were, for the proper anthe- 

 ridial structure. This occurs most distinctly in marginal antheridia (figs. 27-32). 



The antheridial structure, at first consisting of a simple cell, exhibits a considerable 

 collection of protoplasm occupying the greater part of its cavity ; but this portion soon 

 becomes denned by a circular wall, which makes its appearance simultaneously all round 

 the central contents, converting the simple cell into a compound organ, consisting of a 

 central cell surrounded by an annular cell ; while a horizontal septum is formed above 

 and at right angles to this, cutting off a new cell, convex above and flat at the surface, in 

 contact with the contents. 



In antheridia produced on young prothallia, the enveloping tubular cell surrounding 

 the central cell (the parent-cell of the sperm-cells) does not always undergo further sub- 

 division, but in fully developed specimens (when the basal, peduncular cell is often absent) 

 the tubular cell appears to be divided into two by a horizontal septum running all round. 

 This wall is seen most clearly in old antheridia which have discharged their contents 

 (figs. 48, 49). 



The central cell meanwhile acquires an increased quantity of protoplasm, which also 

 appears to become more dense ; these contents by their increase cause the walls of the cell 

 to bulge out in all directions, and at a certain stage they seem to press so much upon the 

 inner wall of the annular cell, forming the boundary of the central cell, as to push it quite 

 against the outer wall, in fact so as to flatten the boundary cell, and for the time to efface 



