28 STRUCTURE AND LIFE-HISTORY OF HAY-SCENTED FERN. 
In the following table the depth is measured from the ridge of entrance down to 
the deepest dorsal focus. The stoma was closed by displacing water with alcohol. 
Open. Closed. 
“ Kb 
Width of stoma........0... 0c 30 ; 28.5 
Width of guard-cells...... ....... 13.5 to14 14 tOoT4.5 
Width of pore... cseeeceeceeees 2.5 ° 
Length of stoma as 44 45 
Depth of stoma............ sane 17 Id 
[p- 350] The first effect of the alcohol is to widen the pore, which then gradually 
closes, the sides becoming apparently straight before they meet. The increase in depth 
at the ends, which is partly responsible for opening the pore of this stoma, works to 
better advantage than in the stoma of Osmunda. 
The cells of the lower epidermis (fig. 111) are smaller and more wavy 
than those of the upper surface. All of the epidermal cells contain chloro- 
plasts, but they are especially abundant in the guard-cells. The thickness 
of the lamina runs from 0.06 mm. at the veinlets to 0.09 mm. where the 
mesophyll is well developed. The air-spaces are especially large in the 
lower half of the spongy parenchyma. A continuous layer of irregular 
cells lines the upper epidermis, but there is nothing that could be called 
palisade tissue (fig. 113). 
Scattered plentifully all over the leaf are hairs of two kinds—acicular 
(fig. 258, 6) and glandular (figs. 105, 113, 249). The first are simple, acute, 
septate, often 1 to 2 mm. long. The latter are simple, septate, with a 
spherical terminal cell, and from 0.08mm.to1lmm.long. The terminal cell 
(or sometimes two cells) is surrounded by a globule of secretion. In this 
doubtless resides the ethereal oil which gives the characteristic scent to 
the plant. Waters (1903, p. 290) states that the odor is stronger in plants 
grown in dry, sunny places than in those grown in shade, and that it is 
changed and intensified in drying the leaves. By ‘‘distilling with steam’’ 
a ‘‘considerable quantity of the partly dried ferns, . . . two or three 
drops of oil were obtained ... It hada rather disagreeable odor, but 
when a drop or two of a solution of the oil in a large amount of ether was 
put on paper and the ether allowed to evaporate, a very pleasant reminder 
of ‘new-mown hay’ resulted’’ (Waters, 1903). One bottle of fronds pre- 
served in 50 per cent alcohol has retained the odor strongly, and it adheres 
very persistently to hands or clothing after the alcohol has evaporated. 
The leaf-shoot, several times referred to above, attracted my attention 
in the fall of 1901. Itis the stem which comes off from the base of the petiole 
(fig. 4). About 20 per cent of the leaves bear such shoots, the remaining 
80 per cent showing no trace of them whatever. The shoot arises on the 
side of the petiole at a very early stage of development, but I was not able 
to find its relation to the sectioning of the segments of the leaf. I believe 
