CELLULAR CONSTRUCTION 



[CH. 



meanwhile the points of interest are the delicacy of the unicellular origin, 

 and the regularity of the cleavages. It thus appears that in the Lepto- 

 sporangiate Ferns all the points where tissues originate show a definite 



Fig. T05. Drawings of the actual segmentation at the margin of leaves of Leptosporangiate Fern^. 

 A = Trichomanes radicaus; B^TrichoDianes renifortne ; C ~ A spleniuin rcscctiiDi; D = Scolopeii- 

 drium vulgare. The last is the most usual type. A and B are characteristic of Filmy Ferns. 



e f g 



Fig. 106. Diagrams illustrating the segmentation of sporangia in various 

 Ferns, a = Polypodiaceae (compare Kny, Wandtafeln XCiv). b=Cera- 

 topteris (compai-e Kny, Parkeriacceii, Taf. xxv, Fig. 3). c = Alsophila 

 (compare Land Flora, ¥\g. 334). d=Schizaea (compare Prantl, Taf. V, 

 Fig. 69), or Thyrsoptcris (Land Flora, Fig. 329), or Trichomanes (com- 

 pare Prantl, Taf. v. Fig. 92). e,f= Todea (compare Land Flora, Fig. 

 ■^QS)- g=Angiopteris (compare Land Flora, Fig. 284). 



method of segmentation. In the apices of the stems, leaves, and roots a 

 single initial cell, with a definite succession of segments cut off from it as 

 it slowly grows, is a constant feature. Such segmentation originates in the 



