XIII] THE DEVELOPMENT OF THE SPORANGIUM 



245 



those sporangia where the first segmentation is transverse, as it is in 

 Dryopteris, either of two things may happen. The stalk-cell may undergo 

 divisions by longitudinal cleavages, thus giving rise to the three-rowed stalk 

 so common in Leptosporangiate Ferns. 

 Or it may remain undivided. The former 

 is seen to occur in Dryopteris, as de- 

 scribed by Muller (Fig. 1 5, 3). The latter 

 occurs frequently in advanced types, in 

 which, as in Scolopendriuni, Aspleniuiii 

 Trickomanes, or Phlebodiuin mtreum, the 

 long stalk consists of a single row of 

 cells (Fig. 239). In such cases the more 

 complicated segmentation of the spor- 

 angial head may result in the upper 

 region of the stalk being still three- 

 rowed. The relation of this to the initial 

 segmentation is suggested by what is 

 seen in Phlebodiuin aureuni (Fig. 240, 

 a—f). Here the first cleavage of the 

 primordiuni is by an oblique wall {a,b,c), 

 which may extend below the level of 

 the epidermal wall {b,c)y or be clearly 

 above it {a). In the latter case growth of the stalk without further segmen- 

 tation, as in {e), would give the condition of the sporangium seen in Fig. 239 

 of Asplenium. 



Fig. -239. Sporangia of Aspleniwu Tricho- 

 Hianes, L., after C. Muller, showing stalk of 

 a singe row of cells. { x 140.) 



Fig. 240. Stages a— ^^ illustrating the development of the sporangitnn 

 in Phlebodiuin aureutn. Compare text. ( x 200.) 



