206 



GLEICHENIACEAE 



[CH. 



consists of a central group of cells surrounded by a peripheral series: it is 

 thus thicker than in ordinary Leptosporangiate Ferns. The sporangium of 

 G. linearis is more elongated, and smaller, and the stalk is thinner, and has 

 no central group of cells. G. flabellata holds a middle position between 

 these two types as regards size and shape, but it will be seen that the num- 

 ber of the spores produced in each sporangium is much higher than in 

 either of the above species, though the spores are individually smaller than 

 in Eii-Gleichenia. 



The sorus of G. flabellata arises as a smooth outgrowth opposite a vein 

 (Fig. 490, a), a considerable number of cells being involved in its origin. 

 Having grown to a height almost equal to the thickness of the pinnule it 



Fig. 489. «-/' = sori of Glcicheuia dichotoma Willd. a-c, show sori of radiate type, but 

 with one or more sporangia in the centre, which is usually in this genus vacant. 

 /, g, h, show states of apparent fission of the sorus. {a-h x about 14.) i,j, k, sporangia of 

 Gleichenia circinata Sw., seen from different aspects: x, is the line of dehiscence: in 

 k the broken stalk faces the observer. ( x 50.) /, m, n, sporangia of Gleichenia dichotoma 

 Willd., seen from different aspects. Note the difference in size from G. circinata. ( x 50.) 



becomes flattened at the apex. The convex margin then begins to grow 

 out as rounded processes which develope into sporangia {b). There is some 

 variety in the segmentation according to the size of the future sporangium. 

 In the larger type of G. flabellata, or in G. circinata, a conical sporangial 

 cell (x) is formed: in it successive oblique divisions follow without exact 

 rule of sequence, the earlier of which go to form the massive stalk {b, c): 

 the later define the central cell laterally, w^hen a periclinal wall follows 

 cutting off the cap-cell. This last appears at a time when the sporangial 

 head projects but slightly from the surface of the receptacle, a state 

 reminiscent of the Eusporangiate Ferns. Thus the whole sporangium is 

 relatively massive, and results from segmentations more numerous than 

 those seen in ordinary Leptosporangiate Ferns, though the last segmenta- 

 tions follow a sequence usual for them. 



