H. Mohl on the Formation of the Stomata.. 207 



researches on the development of stomata. He has shown 

 that they are developed in two different modes. First, there 

 is found, in the epidermis, at the period of formation of 

 a stoma, a little cavity, the bottom of which is occupied by 

 an epidermal cell, which is surrounded by four other cells. 

 By the absorption of this central cell the opening of the 

 stoma is produced. This is the usual mode of development 

 on the foliaceous expansions of the Marchantia. Upon the 

 floral peduncles, on the contrary, the development generally 

 takes place in an entirely different manner. The bottom of 

 the cavity is formed by from three to five wedge-shaped cells, 

 which touch each other at the centre, and which at a later 

 period separate in such a manner as to show an opening in 

 the form of a star. The cells always contract more towards 

 the exterior, being transformed into an obturator ring, whilst 

 the epidermal cells placed around form the margin of the 

 stoma. 



There is evidently a defect in this explanation of the de- 

 velopment of the stomata, as it is not explained how the same 

 form of stomata can originate in two such different ways. 

 Indeed, in the first case, we cannot conceive how the porous 

 cells, which constitutes what Mirbel calls the anneau obtu- 

 rateur, are formed. If the stoma is formed in consequence 

 of the absorption of the epidermal cell, and the surround- 

 ing epidermal layers form the margin, the stoma would be 

 formed only of a simple opening. This however is not met 

 with in nature ; for inwardly, at the margin, two or more 

 cells (porous cells) are seen, which enclose the stoma itself. 

 The origin of these porous cells is explained by the second 

 manner of development described by Mirbel, but it is not in 

 the first case. 



I have endeavoured to solve the question by examining the 

 Marchantia polymorpha, but I have not been successful, 

 because in this plant the examination of the epidermis in its 

 youngest state presents very great difficulties, as it can only 

 be taken off by means of a scalpel, and does not therefore 

 admit of being separated free from the subjacent parenchyma. 

 In this way some of the subjacent parenchymatous cells are 

 always removed with the epidermis, and prevent our recogni- 

 zing with the necessary precision the slight changes which 

 take place in the stomata at the moment of their production. 



Respecting these researches, I shall confine myself there- 

 fore to merely stating, that I have seen the stomata originate 

 on the frond of the Marchantia in the second mode pointed 

 out by Mirbel, but I have not succeeded in seeing any sto- 

 mata originate from the absorption of a cell. 



