XXIl] 



SPORE-PRODUCING MEMBERS 



165 



sections be cut of these when very young the characteristic segmentation of 

 the sporangia is seen in the marginal cells (Fig. 448, C, D) ; but very soon 

 strong growth and division spring up in adjoining cells, forming a false 

 margin of indusium {E, F, G), by which the sporangia are forced towards 

 the midrib, and assume a falsely superficial position. Onerow of them appears 

 on each side of the midrib in \Eu-Schizaea, and yLopJiidiiim (Fig. 441, A). 

 But in \ActinostacJiys there are four rows. This is a consequence of a re- 

 adjustment during development of a single series on each side. The two 

 rows arise from a single marginal row of cells, but as the sporangia grow they 

 are alternately pressed out of line right and left, and consequently two rows 

 of them appear on each side of the adult pinnule (Fig. 449). The origin of 



(X 



Fig. 449. a, b. Longitudinal sections following the marginal series of cells of 

 the pinna of Schizaea digitata, and the sporangia that arise there. In [a) they 

 are cut vertically, in (i^) horizontally. The latter shows the origin of the two 

 rows of sporangia from a single margin. ( x 85.) 



the sporangia is also proved to be marginal in Anemia, but as the pinnule 

 is flatter they are more exposed than in Schizaea, appearing falsely super- 

 ficial as before (Prantl, I.e. p. 39; also Stevens, Ann. of Bot. xxv, p. 1059). 

 Perhaps the most interesting genus of all is Mohria, for here a single 

 sporangium is formed near to the end of each vein, while a marginal flap 

 grows from below it, and covers it like a separate indusium (Fig. 441, D). 

 Here again the development shows that the origin of the sporangium is 

 marginal, but it is thrust to an apparently superficial position by a strong 

 growth below the stalk on the upper side. The result is shown in Fig. 450, 

 Thus it appears for all the genera that the origin of the sporangium is 

 actually marginal. In order to bring the leaves of the Schizaeaceae into 

 relation with those of other primitive F'erns the simplest type of sporophyll 

 may be used, viz., that of the small Brazilian species Anemia (Trochopteris) 



