146 ORIGIN OF STOMATES. [ BOOK * 



The origin of stomates lias always been very obscure. 

 Schleiden considers them to be the last cytoblasts which the 

 epidermal tissue forms (see page 33 for his theory of cyto- 

 blasts). He considers that in the beginning all the forms 

 of tissue are, in shape, contents, and structure, exactly the 

 same, and that all the modifications of tissue take place later. 

 He supposes that the exterior tissue of a given mass ceases to 

 produce new cells in its interior sooner than that of the 

 exterior, and that consequently epidermis is first completely 

 organised; but in the epidermis some of the cells retain 

 longer than others the property of forming internal cells, 

 and it is when the last pair of cells separates and absorbs their 

 parent that the stoma is produced. The cells forming the 

 stomatic sphincter are in their origin exactly the same as the 

 cells of the parenchym, and they remain so in their functions 

 throughout their whole existence. 



Mohl gives the following account of their origin in the 

 Garden Hyacinth : 



" I selected these leaves," he observes (Annales des Sciences, 

 2 ser. xiii. 23) "not alone because their stomates are pretty 

 large, but because these leaves allow, from their growing from 

 above downwards, observations to be made on the same leaf 

 on all the phenomena presented by the development of the 

 stomates. Indeed, these organs are perfect in the upper 

 and older part of the leaf, when they are not to be found 

 at all in the lower and younger part, which is in the bulb. 

 In the lower part of the leaves and between the cells of the 

 epidermis, smaller quadrangular cells are seen, the transversal 

 diameter of which is a little longer than the longitudinal 

 diameter. These cells, as well as those of the epidermis, are 

 colourless. Sometimes they are empty, at others they inclose 

 a slightly granular mass. Higher up, towards the apex of the 

 leaf, this granular substance is found united into a globular 

 mass, which is, however, frequently ill defined. At the same 

 time a partition is formed in the middle of the cell and in the 

 longitudinal direction of the leaf. This partition is at first 

 but slightly distinguishable; but the lines which limit it 

 soon become as visible as those which mark the sides of the 

 cells. This partition now begins to unfold ; the first trace of 



