14 Britton and Taylor : Life History of Schizaea pusilla 



The stomata are restricted to two rows of epidermal cells and 

 almost every epidermal cell in these rows gives rise to one (Fig. 

 82). A cell of the epidermis before it has lengthened forms a U- 

 shaped wall at the upper end of the cell (Figs. 86, a, b) ; the points 

 of the U meet the radial wall which separates this cell from the 

 one next above (Fig. 86, b) ; this cell becomes the mother cell of 

 the stoma, and by growth presses the partition wall back a short 

 distance into the upper epidermal cell (Fig. 86, c). This cell 

 divides by a tangential wall into two cells of equal size ; these 

 become the guard cells (Fig. 86, c, d) each containing abundant 

 chlorophyl. These guard cells enlarge considerably (Fig. 86,^, e) 

 so that they are raised above the epidermis as shown in an oblique 

 view (Fig. 83). The wall between the guard cells splits along its 

 central portion making an opening to the space below ; the epi- 

 dermal cell meanwhile has lengthened and the cell above has 

 formed a stoma in the same way. The leaf bundle is more nearly 

 collateral than that of the stem ; the xylem faces the ventral, the 

 phloem the dorsal surface of the leaf (Figs. 88, 90). There is a 

 two-rowed endodermis around the bundle ; the epidermal cells are 

 large and in some instances occupy one half of the cross section. 

 The ground tissue is made up of thin-walled parenchyma with 

 numerous air spaces (Fig. 89) and the cells contain chlorophyl. 



Sporophyll 



The sporophyll is very similar to the sterile leaf with the excep- 

 tion of the formation at its apex of pinnae bearing the sporangia ; 

 these have been carefully studied by Prantl and others in several 

 species of Schizaea, the descriptions of which, from present obser- 

 vations, appear to hold good for Schizaea pusilla. One of the 

 largest sporophylls measured 1 3 cm. from base to apex, the por- 

 tion bearing the pinnae was 6 mm. long and eight pinnae were 

 formed on one side and seven on the other ; the longest pinna 

 measured 4 mm., of this 2^ mm. is the portion which bore the 

 sporangia. The lowest pinna on each side had formed four spo- 

 rangia each, the others eight each. Prantl figures six sporangia 

 for Schizaea dichotoma, and sixteen for Schizaea Penmda. The 

 edge of each pinna rolls up over the sporangia, forming an in- 

 dusium, and the end cells at the summit and also along the mar- 



