THE EPIDERMAL TISSUE. 
are applied to one of its side-walls (Fig. 84). Not unfrequently, especially with Ferns, 
e.g. Asplenium bidblferum. Pteris cretica, Cibotium Schiedei, &c., preparatory cells are 
cut out in this manner from the epidermal cell before the formation of the mother- 
cell, out of which the guard-cells are then formed by simple longitudinal division. 
In consequence of the U-shape of the division-wall which separates the mother- 
cell of the stoma from the epidermal cell, the former is half, or more than half, en- 
closed by the latter when looked at from above. In some Ferns and Sileneae the wall of 
the mother-cell of the stoma is from the first so strongly curved that it touches the epi- 
dermal cell only in a narrow band ; in Anemia -villosa it touches it only at one spot, the 
partition-wall seen from above appearing like a circle. In Anemia densa ^x\d fraxinifolia 
the side-wall of the epidermal cell does not anywhere touch the wall of the mother-cell 
of the stomal When first formed this cell has the form of a hollow cyhnder, or, 
more exactly, of a truncated cone, the base and truncated end of which are portions 
of the upper and lower wall of the epidermal cell ; out of the latter a cell is thus 
cut oat like a piece out of a cork by a corkborer ; this piece is the mother-cell of the 
Fig. Sy.-SLiperficial view of a stoma of Ajiemia fraxuii- S parenchyma of the leaf containing chlorophyll. 
Jblia with the epidermal cell completely surrounding' it ; e epi- 
dermis, ss guard-cells ; cl chlorophyll-granules. 
stoma; and thus arises the remarkable arrangement represented in Fig. 87, where, as 
may be seen, the two guard-cells are entirely enclosed within a single epidermal 
cell. Similar, but more complicated, is, according to Rauter, the structure in Nipbo- 
bolus Lingua. 
By further growth of the guard-cells and of the epidermal cells which surround 
them, different relative positions of the former to the surface may be brought about ; 
the guard-cells may, when mature, lie in one plane with those of the epidermis, or may 
be deeply depressed and apparently belong to a deeper layer of cells (Fig. 88) ; some- 
times they are, on the contrary, elevated above the surface of the epidermis. 
The stomata of Marchantieae may shortly be mentioned here in connexion with 
what has already been said on Fig. 65, p. 78. After the formation of the air-cavities, 
which are filled with outgrowths containing chlorophyll (Fig. 89, A, chl), one cell of the 
Strasburger, in Jahrb. für wiss. Bot. VII. p. ,^93 ; also Rauter, /. c. 
