208 H. Mohl on the Formation of the Stomata. 



To make amends, I think that I have observed A^ith suffi- 

 cient precision the formation of the stomata on the leaves of 

 the Hi/acinthus orientalis. I chose these leaves, not only be- 

 cause their stomata are of considerable size, but because by 

 their growth from above downwards, it is easy to observe, on 

 the same leaf, all the series of facts which the stomata pre- 

 sent in their development. These organs, indeed, are already 

 perfectly developed on the higher and oldest part of the leaf; 

 M hilst, in the lower part, newly formed and still enclosed in 

 the bulb, they do not yet exist. 



It is in this lower part of the leaves and between the epi- 

 dermal cells that smaller quadrangular cells maybe observed, 

 the transverse diameter of which is a little longer than the 

 longitudinal. (PI. II. fig. 1, «, a.) These cells, as well as 

 those of the epidermis, are colourless. Sometimes they con- 

 tain nothing, and sometimes they enclose a slightly granular 

 mass. 



Higher up, towards the apex of the leaf, this granular sub- 

 stance is met with collected in a round mass, which frequently 

 however is not clearly defined. At the same time a partition 

 forms in the middle of the cell and in the longitudinal dii'ec- 

 tion of the leaf At the beginning this partition is but slightly 

 indicated (PI. II. fig. 1, b) ; but soon the lines that limit them 

 are as clearly drawn as those which mark the lateral walls of 

 the cells (fig. 2, a). 



This partition now begins to double ; thus the first trace 

 of a stoma establishes itself, and the cell, originally simple, 

 divides and fonns the two cells of the pores. 



In the course of the development, the cells which suri'ound 

 the pore enlarge, and the central slit enlarges in a still greater 

 proportion. The grumous mass is always found accumulated 

 on the inner w alls of these cells, and communicates with the 

 other walls of the cells by means of filiform processes (fig. 3.)*. 



Lastly, in the perfectly developed stoma (fig. 4.), the gru- 

 mous mass contained in the cells which form the border of 

 the pore is equally distributed in their interior, where the 

 grains of chlorophylle are likewise formed. 



The development which I have just described takes place 

 very regularly in each stoma, but the same part of the leaf 

 does not always exhibit stomata at the same stage of deve- 

 lopment. Certain stomata frequently outstrip others close 

 beside them. 



* These thi'eads, which unite a mucous mass situated in the cellular cavity 

 with the cellular partitions, are met with not only here, but they are often 

 found elsewhere; for example, in the hairs of the yoxuig stalks of fioiirds, 

 and in the articulations oi Zygnema. 



