4 ERNST ANTEVS, THE SWEDISH SPECIES OF PTILOZAMITES NATH. 
their number and the thickness of the cuticle. If the latter is comparatively thin, 
there are, as a rule, no stomata or only a few, and vice-versa. 
In various species there are small holes in the cuticle (pl. 3, figs. 7, 11). They 
occur on both the lower and the upper side of the frond, and in some cases go 
straight through the segments. It is obvious that they were formed while the plant 
was still living. They vary somewhat in size, and are generally quite round. The 
bordering cells are more strongly cutinized than the rest of the epidermis. In some 
cases regeneration of the cuticle has taken place at the sites of former holes, but it 
has not attaimed ordinary thickness (pl. 3, fig. 11). 
In another paper (1914 a, pp. 6, 12) I have described similar holes in Lepidopteris 
Ottonis (GÖPP.) ScHIMP. and ÅAntholithus Zeilleri NATH. There I expressed the suppo- 
sition that the holes had probably been caused by a parasitic fungus, and I am in- 
clined to apply the same explanation here. TIt is, however, also possible that they 
were caused by insects. 
I have already given an account of the distribution of the stomata. The 
guardian cells were sunk below the epidermis as in other and analogous Xerophytes. 
At times it is possible to discern remains of them (pl. 2, fig. 9). The round holes 
(pl. 1, fig: 7; pl. 2, figs. 7, 9) seen in the cuticle are the entrances to the stomata. 
The walls of the subsidiary cells which border these entrances form a ring, which 
is sometimes rather thin, and sometimes considerably thick. These stomata differ 
from those in Thinnfeldia and others principally by the ring mentioned and by the 
fact of the subsidiary cells not having a regular shape. It is true that the differ- 
ence is sometimes rather striking, but, on the other hand, it is evident that it is 
only of a superficial nature. 
In the recent plants which I have had the opportunity of examining, I have 
not found any stomata of the same structure; but, on the other hand, I have found 
such in the closely related fossil Ctenopteris cycadea (BRNGN.) and COt. Leckenbyi 
(LECKENBY ex BEAN's M.S.).' 
Earlier KNOWLTON (1895, p. 387; figs. 1—3) described similar stomata in Pa- 
laeohillia Arkansana KNOWLT., also a fossil plant. KNOWLTON explains the surround- 
ing cells quite correctly as ordinary epidermal cells, but believes he has found 
under each of them another, on the whole corresponding cell. These latter cells he 
regards as the guard-cells of the stoma. The number of guardian cells should accord- 
ingly vary from four to six. 
Later on HoLmM (1896, p. 208) discusses the same fossil, and tries to show that 
KNOWLTON's opinion cannot be right. He points out that the guard-cells can hardly 
1 The cuticle of Ctenopteris Leckenbyi was quite recently examined by THomas & BANCROFT (1913, p. 
194); and I have nothing to add to the description given by them. The stomata agree with those in Ptiloza- 
mites, though the ring bordering the entrance is as a rule thicker. 
Of Ctenopteris cycadea I have examined two fragmentary specimens from Pålsjö in Scania. The cuticle 
is very thick, and is thicker on the upper side than on the lower. On the upper side the cells have very sharp 
corners, and are rhombic, square, or rectangular; on the lower they are of an isodiametrically polygonal shape. 
Faint traces of veins can be discerned on the lower side. Stomata occur here fairly numerously but are very 
rare on the upper side. They are of exactly the same structure as those in Ct. Leckenbyi. 
