xxiv] 



SPORANGIA 



209 



distal face (the plate) is small as in Sc/iisaea, while occasionally it is partially doubled. The 

 spore-output is large, counts of "about 480" and "at least 416" having been made 

 (Thompson). It thus falls in this character between G. flabellata and other species 

 observed. Platyzoma is also peculiar in the variability of structure of the sporangium, as 

 well as in the inconstancy of size and number of the spores (Fig. 492). The annulus is 



^^-^ 



Fig. 491. .-:/= section of a sporangium of GleicheniaJlabeUata, showing 

 over 60 spore-mother-cells in section, (x 100.) j5 = spore-mother- 

 cells of the same, older and separated from one another in the tapetal 

 Plasmodium. (X165.) C = spore-motlier-cells and tapetal Plas- 

 modium of Gleichenia dichotonia : only 20 are seen in section. ( x 100.) 

 jO = cells separated in tapetal plasmodium. ( x 165.) 



Fig. 492. Sporangia of Platyzojua, all of same magnification ( x 24), showing variability 

 in size and structure, i, ii, are extremes of difference in size, with oblique annulus, as 

 in Gleichenia: iii, annulus irregular : iv, annulus almost transverse: v, annulus nearly 

 vertical, interrupted at the stalk: vi, vii, ruptured sporangia, with 3-rowed stalk: 

 viii, ditto with 4-rovved stalk. The stomium is not strictly defined, but the dehiscence 

 is lateral. (After J. M'^L. Thompson.) 



sometimes nearly horizoiital, sometimes nearly vertical, and the sequence of its cells is 

 very irregular. The stalk is typically three-rowed, but four-rowed stalks occur. The 

 insertion of the stalk frequently interrupts the annulus, as it does in many Leptosporangi- 

 ate Ferns, while the point of dehiscence, which is defined by a thin-walled, but not highly 

 differentiated stomium, is clearly lateral. It thus appears that the sporangial structure of 

 B. II 14 



