THE EPIDERMAL TISSUE. 



87 



apparently irregular. The number of the stomata is generally extraordinarily great 

 in the epidermis of organs containing chlorophyll ; A. Weiss counted on one square 

 mm. in 54 species examined i-ioo stomata, in 38 species 100-200, in 39 species 

 200-500, in 9 species 4oa-5oo, and in 3 species 600-700 stomata. The origin of 

 stomata is always the result of the formation of a mother-cell, first of all by division 



Figs. 73-75. — I'onu.Umn of the stoin.-ila of ihc loaf of Hyacinthtis nrientalis, seen from the surface (Xoi;)o) ; tlie preparations were 

 made from leaves, wliich were at first 3-4 cm. long ; they were obtained simply by removing the epidermis ; e always signifies the 

 cpidennis-cells, S the stoma. The order of development is Fig. 73, A, S' , S", S'" ; then Fig. 74, A, />, and finally Fig. 75. In Fig. 73, 

 fi, a piece of cpidennis is represented with the mother-cells of the stomata already divided, after extraction of the protoplasm by 

 solution of pot.ish and acetic acid. Preparations of this kind show most distinctly that the partition-wall never grows from without 

 inwards ; it is either entirely absent or present along the whole surface. Fig. 75 shows the guard-cells after treatment with potas- 

 sium odidc ; the protoplasm has contracted ; the stoma is not yet perfectly developed. 



of a young epidermis-cell, which is sometimes preceded by several preparatory 

 divisions in it or in the adjoining epidermis-cells ; and this mother-cell becomes more 

 and more rounded off, and the guard-cells of the stoma are produced from it by 

 division. The variety of these processes up to the point when the opening itself 

 appears, can hardly be explained in a few words ; I prefer therefore to describe some 

 examples more minutely. One of the simplest is afforded by the development of the 

 stomata on the leaf of Hyacinthus orientalis, which has already been depicted in 

 transverse section in Figs. 61-64 (p. 75); these the reader must compare with 

 Figs. 73-75, which represent the process seen from the surface. The preparation for 

 the formation of the stoma is here very simple: — a nearly cubical piece of a long 

 epidermis- cell (Fig. 73, A, S, S") is separated by a septum, and this is the mother-cell of 

 the stoma. It is divided by a longitudinal wall (/*. e. by one lying in the direction of 

 the axis of growth of the leaf, and standing at right angles to its surface) into two equal 

 cells, which round themselves off as they grow. The manner in which the opening 

 follows the partition-wall has already been described in Figs. 61-64, and can nov/ easily 

 be understood with help of the superficial view in Fig. 74. In Equisetum Hmosum a 

 similar appearance to that represented in Fig. 73 shows itself immediately after the 

 first formation of the mother- cells of the stomata; but the mother-cell undergoes in 

 these cases three divisions, first one obliquely to the right, then one obliquely to the 

 left ; finally the tniddle one of the cells which originate in this manner is bisected by a 

 wall standing at right angles to the surface. Four cells thus arise in one plane, of which 

 the two outer ones grow more rapidly, while the inner are forced downwards and 

 come to lie beneath them; the stoma then appears, when perfect, as if it had been 

 formed according to the Hyacinthus type, in which each guard-cell has been again 



