XIII] 



SPORE-OUTPUT 



265 



Sections of the sporangia of Ferns transitional between the Eusporangiate 

 and the Leptosporangiate types support the spore-counts which are transi- 

 tional also. For instance, a vertical section of a sporangium of Osmunda 

 (Fig. 259) traverses 30 to 32 spore-mother-cells. The sporogenous group is 



Fig. 258. Spores of Platyzonia, after 

 M'^Lean Thompson, all drawn to 

 the same scale, a, one of the 

 largest; (^, of medium size; f, one 

 of the smallest. ( x 26.) 



Fig. 259. Sporangium of Os- 

 munda regalis, L., containing 

 a large sporogenous tissue, sur- 

 rounded by a tapetum con- 

 sisting in parts of three layers 

 of cells. (After von Goebel.) 



spherical, and the diameter of each cell is about one-sixth of the whole sphere. 

 Accordingly their total number would approximate to 128, which accords 

 with an estimate of 5 1 2 spores. It has moreover a tapetum widened at places 

 to three layers, and a massive stalk (Fig. 243, d, e). All these points are transi- 

 tional between the Eusporangiate and the 

 Leptosporangiate types. Again mLygodhim, 

 with a spore-output of 128 — 256, the section 

 of a sporangium shows about 20 spore- 

 mother-cells. Here also there are irregularly 

 three layers of cells between the sporangial 

 wall and the sporogenous group, while the 

 stalk is relatively massive (Fig. 260). In the 

 genus Gleichenia, including G. flabellata with 

 relatively large spore-output (512 — 1024), 

 and G. dicJiotonia with relatively small output 

 (256 or more), sections again bear out the 

 spore-counts (Fig. 261, A — D), while the 

 thickness of the stalk follows suit (Fig. 243, 

 a, b). In those Ferns with numbers below 64 

 the stalk is always thin and, as has been seen, may fall to a single row of cells 

 (Fig. 239). Lastly, the mechanism of the annulus is essentially an opening 

 mechanism in the larger types, and nothing more. But in the sporangia with 



Fig. 260. Section through a sporangium 

 oi Lygodium cii'cinatum, after Binford. 

 20 spore-mother-cells are cut through : 

 the tapetum is more than doubled. 

 (X480.) 



