Ceratopteris thalictroides , (L) 103 
composed mainly of spongy parenchyma with large air-spaces. 
The epidermis is made up of large thin-walled cells which 
have a sinuous outline when seen in surface-view. Stomata 
are present on both sides of the leaf in the sterile forms ; they 
are also present on the fertile leaves on the upper side in fairly 
large numbers, but they are less numerous on the under 
surface. Seen in transverse sections of leaves (Fig. 5) the 
stomata have a very curious appearance. A large air-space 
lies immediately below the opening and the guard-cells have 
a curious beak-shaped projection. This is found on the inner 
face of the guard-cells, i. e. the side which is turned towards 
the other guard-cell, and at the topmost corner of this side. 
The neighbouring epidermal cells which border immediately 
on the stoma are somewhat smaller in size. As in Salvinia 
and Azolla the guard-cells are but feebly cuticularized, but in 
regard to their shape and beak-shaped projection there is 
a strong resemblance to those figured and described by 
Haberlandt 1 in Lemna. 
The steles in the sterile leaves are very numerous and 
anastomose largely, forming a conspicuous network which is 
easily seen. Trabeculae of parenchyma are found bridging 
over the air-spaces between the vascular bundles and passing 
across from the epidermis on the upper side of the leaf to that 
on the lower. The bundles in the fertile leaves are five in 
number and are comparatively small. Where a bundle 
occurs, more parenchymatous tissue is found surrounding it 
on all sides. Each stele consists of a group of tracheids 4-8 
in number, the xylem frequently abutting directly on the 
pericycle. The phloem is feebly developed and cannot be 
distinguished from ordinary parenchymatous cells. The 
endodermis and pericycle are again very conspicuous. 
B. The Stem. 
a. The mature Plant. The steles in the stem are of two 
kinds, a ring of large conspicuous steles (Fig. 3, b^) being 
ranged round the periphery, and within this ring a number of 
1 Haberlandt, 1896, p. 401 , 
