FORMATION OF THE COMMON WALL OF CELLS. 



77 



taken place ; the partition-wall is formed ', and appears as a very thin simple lamella, 

 which soon thickens, and especially where it meets the wall of the mother-cell (Fig. 

 62, J). The thickening-mass appears at first quite homogeneous; afterwards an 

 indication of stratification is to be observed, and the first trace of a separation into 

 two (Fig. 62, J5). In Fig. 63, t, the splitting is already completed; the growth of 

 the separated lamellae now proceeds in a peculiar manner, so that a cleft arises 



Figs. 61-63.— Development ot the stomata in the leaf oi Hyacinthics orientalts, seen in vertical section (X ! 



which is narrower in the middle, wider without and within, and which connects the 

 intercellular space / (the stoma) with the external air (Fig. 64). It is worth mention 

 that before the division of the mother-cell an obvious cuticle has already over- 

 spread it together with the adjoining epidermal cells. This cuticle is easily 

 recognised in the condition B, Fig. 62, while still continuous; by the sphtting 

 of the partition-wall into two lamellae it finally becomes ruptured (Fig. 63), and 

 by the cuticularising of the outermost layer 

 of the now separated lamellae it is afterwards 

 continued over the surfaces of the cleft (Fig. 

 64). If the process of the formation of the 

 stoma is followed in a front view, it is seen 

 that the splitting of the partition- wall does 

 not extend throughout, but that a portion 

 still remains undivided at each end where 

 it adjoins the original mother-cell-well. The 

 two cells which enclose the cleft, or Guard- 

 cells^ are not only distinguished from the 

 other epidermal cells by this peculiar mode ^^' ^' 



of division and of growth ; they also differ from them in containing chlorophyll and 

 starch. 



(2) In the family of Marchantieae belonging to the Hepaticae, the origin and 

 structure of the stomata (Fig. 65, 5, sp) is much more complicated; of this we must 

 speak hereafter. Here it need only be pointed out that even before the formation 

 of the stoma the epidermal cells become detached from those lying beneath over 

 rhomboidal areas which are marked off from one another by walls formed of cells 

 which are not detached (Fig. 65, jB, ss). These large hypodermal chambers, each 

 of which opens to the outside in its middle by a stoma, are destined to enclose the 

 chlorophyll-containing tissue of these plants. The layer of cells which forms the 



^ I was unable to detect nuclei immediately before and for a considerable time after the 

 division. [Strasburger has however , succeeded with preparations preserved in alcohol in distin- 

 guishing, in the development of stomata in Iris pumila, the nucleus of the mother-cell and the 

 successive stages of its division; see Ueber Zellbildung und Zelltheilung. p. 115, t. v. figs. 38, 39; 

 French translation, pp. 1 14-1 16.] • 



