248 



MOSSES AND FERNS 



CHAP. 



posed of several layers of cells, and this encloses a cavity in 

 which are the growing point of the stem and the youngest leaf. 

 The leaves here form much more rapidly than in the species of 

 the temperate regions, as the growth continues uninterruptedly 

 throughout the year. The real apex of the stem forms an in- 

 clined nearly plane surface, slightly raised in the centre, where 

 the single apical cell is placed (Fig.T34,A,B). This cell is by no 

 means conspicuous, and not always readily found, but probably 



is always present. It has 

 the form of an inverted 

 three-sided pyramid, but the 

 lateral faces are more or less 

 strongly convex, and the 

 apex may be truncate. From 

 the few cases observed it is 

 not possible to say whether 

 in addition to the three sets 

 of lateral segments basal seg- 

 ments are also formed, but it 

 is by no means impossible 

 that such is the case. Ac- 

 cording to investigations of 

 Rostowzew ( ( I ) , p. 45 1 ) » 

 the apical cell of the stem 

 of OpJiioglossimi viilgatum 

 shows considerable variation, 

 and may be either a three or 

 four-sided prism, i. c, it ap- 

 parently also may have the 

 base truncate. Holle's (i) 



Fig. 133. — Ophioglossum pendulum. A, Me- 

 dian longitudinal section of stem apex, X4; 

 X, the growing point; B, young sporophyll, description agrCCS Avith this 

 X2; sp, the sporangiophore; C, an older ^ *- 



leaf, showing the venation, X2. 



except that he states that he 

 always found the cell pointed 

 below, not truncate. The segments cut off from the lateral 

 faces are large, and the divisions irregular. They are appar- 

 ently formed in very slow succession, and the irregularity of the 

 succeeding divisions in the segments themselves soon makes it 

 impossible to trace their limits. Each segment apparently gives 

 rise to a leaf, but this is impossible to determine with certainty. 

 The first wall in the young segment proba1)ly divides it into an 

 inner and outer cell, but the next divisions could not be deter- 



