764 On the Development of the Stomata of [ October, 
If, however, the younger forms of the stomata are examined, it is 
perceived at once, that what were taken as guard-cells are not 
really such, but are cells corresponding to the accessory cells de- 
scribed in Tradescantia. In the mature leaf the epidermal cells 
are long and narrow, and have a very marked sinuous outline; 
but in the young leaf they are proportionately much shorter, and 
have a nearly straight outline. The formation of a stoma is as 
follows : ‘ 
A vertical septum is formed across the end of a cell, shutting 
off a cell, which is very short (Plate 11, Fig. 1). This cell, however, 
lengthens rapidly, and soon is nearly square in shape. ‘The sto- 
mata are at first formed in rows, but when mature this regularity 
is not very obvious. Almost as soon as the mother-cell of the 
stoma is formed, two small cells, at the sides, are cut out from the 
adjoining epidermal cells, much as in Tradescantia (Fig. 1): 
These at the outset scarcely keep pace with the development of 
the mother-cell; but finally grow much faster, and in the end 
so crowd it as to completely change its shape. The mother-cell 
rounds off and divides, developing for some time very much as 
any ordinary stoma (Figs. ti—vi1); but when it is about half 
grown there is a marked change. The stoma gradually begins to 
lengthen (Fig. 1x), and the accessory cells which have hitherto 
been small and unimportant, begin to grow more rapidly, begin- 
ning also to show their triangular form. The stoma becomes 
more and more elongated, and at this stage is nearly rectangular 
(x), and two or three times as long as broad. Distinct vacuoles 
are usually present and situated at the ends, but these soon dis- 
appear, and their position marks the place of greatest condensa- 
tion. From this time, the accessory cells form the most conspi¢- 
uous part of the stoma. They grow toward the center of the 
stoma, and in consequence the guard-cells become more and more 
contracted, until the stoma itself, instead of being oval, as it was 
when half grown, has become somewhat dumb-bell shaped, and 
to a casual observer, the accessory cells, which are no part of the 
stoma proper, might easily seem to be the guard-cells, while the 
real guard-cells are so altered that they look like mere thticken- 
ings around the pore, 
The shape of the accessory cells varies somewhat, but iS, 
general, approximately triangular, or, rather, three-lobed; but 
sometimes the lobes are so indistinct, that the cells are nearly oe 
in 
