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, 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, B). In Fig. 63, /, 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 of the stoniata in the leaf of Hyacinthus orientalis, seen in vertical section (X 800). 
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 5, Fig. 62, while still continuous; by the splitting 
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 Marchantiea? belonging to the Hepaticae, the origin and 
structure of the stomata (Fig. 65, B, 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, JS, 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 pnmiln, the nucleus of the mother-cell and the 
successive stages of its division; see Ueber Zellbildung und Zelltheilung. p. 115, t. v. figs. 3S., 39; 
French translation, pp. 114-116.] 
\ 
