292 



THE GAMETOPHYTE, AND SEXUAL ORGANS 



[CH. 



or based in the smaller upon actual spore-counts. When the parallel 

 results shown in these columns are compared with the general facts of struc- 

 ture of the Ferns in question, and especially with the details of their apical 

 meristems as set forth in Chapter Vl, they will be seen to give consistent 

 support to the general progression there traced. 



Such comparisons may be pursued further into the early segmentations 

 of the young antheridia. It has been found possible to trace a sequence of 

 steps in the initial segmentation of the sporangia of Eerns, leading from 

 those of the massive Eusporangiatae to those of the delicate Leptosporan- 

 giatae (Fig. 238, Chapter XIIl). The necessary data are not yet to hand for 

 an exhaustive comparison of this nature in the case of the antheridia. But 

 three diagrams based upon drawings from reliable sources may be placed 

 in sequence, as a step towards a more complete demonstration (Fig. 282, 

 a, b, c). Their correspondence with the diagrams a, d, and g, e, of Fig. 238, 

 Chapter XI 1 1, shows the essential similarity of the initial segmentation of the 

 two quite distinct organs, viz. the sporangia and the antheridia. It proves 

 again, if further proof were wanted, that the progression in organisation 

 from the relatively massive Eusporangiate to the delicate Leptosporangiate 

 state is quite general for the various parts. 



A very iiatural concomitant of the diminishing output of spermatocytes 

 is a progressive simplification in structure of the antheridial wall. In the 

 large sunken antheridia of Eusporangiate Ferns the antheridial wall may 

 consist, partially, of two layers of cells, but usually of onl>; one (Fig. 274, e). 

 There may be several opercular cells, as in BotrycJiimn Lunaria, or only 

 one (Fig. 283, A\ In either case the cell is cut out from the distal cap-cell 

 of the antheridium by successive segmentations (Fig. 283, E, F). Similar 

 segmentations appear also in the Cyatheoid Ferns, dividing the cap-cell 

 into two or three, of which the innermost is the single operculum. These 



