EPIDERMIS. 



41 



a. The Initial cell, bounded by a curved, or even U-shaped wall, is again divided by 

 a wall almost similar to the latter into a Mother-ceil and a horseshoe-shaped subsidiary 

 cell (Asplenium bulbiferum ', Pteris flabellata (Fig. 14), cretica-); or successively by 2-3 

 curved walls, which alternate in two directions in the surface, and cut one another, into 

 a mother-cell, surrounded by a zone (or in parts a double zone) of half ring- or horse- 

 shoe-shaped subsidiary cells. The longitudinal axis of the subsequent slit is parallel to 

 the chords of the previous curves of division: Cibotium Scheidei (Hildebrand, I.e. Fig. 

 37-39), Mercurialis perennis, ambigua, Pharbitis hispida, Basella, Pereskia aculenta; or 



Fig. 14.— Leaf of Pteris flabellata, surface vic^v. A very young, e epidermal cells ; v subsidiary cell, s (close to z) 

 mother-cell, the other j initial cell of the stoma. B almost mature, s guard-cells, v and e as in A. From Sachs' 

 Textbook. 



it cuts them at right angles : Thymus serpyllum, Physostegia virginiana, and other Labiata: 

 (Strasburger, /. c). In the last category but one are also the Equiseta. 



b. The Initial cell is divided successively by walls arranged in three directions in the 

 surface into a simple or multiple zone of subsidiary cells, and a mother-cell surrounded 



Fig. 13.— Surface of leaf of Sedum purpurasceus. A young, the initial and subsidiary cells arising by division of 

 the epidermal cells (e) ; in three of the latter the initial cell is just marked off. in four others these are further 

 divided ; the numbers indicate the successive division walls. B almost mature, c and numbers as in A, From Sachs' 

 Textbook. 



by it. With few subsidiary cells : Papilionaceae, Solanaceae, Asperifolise, Cruciferae ; 

 with a large number of them : Crassulacese (Fig. 15), Begoniaceae ^, also Cactacese. 



' Strasburger, I.e. figs. 36-41. 



° Hildebrand, Botan. Zeitg. 1866, Taf. X, fig. 20-23. 



^ Strasburger, I.e. — Compare for details this work so often cited; also the not always precise 

 statements of Karelstschikoff, Zur Entw. der Spaltoffnungen, Bull. Soc. Imp. de Moscou, 1866. 



