Cape Species of Passer ina, with some Notes on their Anatomy. 595 
the groove among the hairs (Fig. 3). The effect is to bring the pore 
slightly nearer the mouth of the groove and to provide a short tube within. 
In neither case can the effect on diffusion be important. When the leaf- 
groove is narrowed, however, the inner epidermis is thrown into folds, and 
I incline to the view that the slightly raised position of the stomata prevents 
mechanical closure of the pores. It may also secure greater freedom of 
opening, as compared with stomata in which the guard cells have to push 
directly against adjacent cells supported by the rest of the epidermis, as 
well as reducing to a minimum any mutual interference of adjacent stomata. 
Fibres. The fact that in P . filiformis the fibres interrupt the palisade 
layer outside the principal bundles has already been mentioned. The fibres 
extend farther, however, spreading laterally between the epidermis and 
Fig. 6. Section through median 
bundle of leaf of P. filiformis , showing 
lateral wandering of fibres hypodermally. 
The fibres drawn near the phloem were 
the only ones that stained yellow with 
chlor-zinc-iodine. 
palisade tissue, where they are seen in transverse sections cut in various 
directions (Fig. 6). This feature is more strongly marked towards the tip, 
less strongly towards the base of the leaf. 
The small size of the leaf and very small diameter of the fibres (5-10 \x) 
make it difficult to follow the wanderings of the fibres in sections. Boiling 
for a few minutes in Schulze’s macerating solution makes it possible, 
however, to remove the epidermis from both sides, and preliminary 
observations have been made in this way. 
In young leaves, associated with the minor veins, fibres of the usual 
type can be seen, slender and tapering to a point at both ends (Fig. 7). 
Near the tip in young leaves and extending towards the base in older leaves 
is found a sub-epidermal sheath of wandering fibres quite different in 
character. Their tips are often slightly swollen and club-shaped. Their 
growth is clearly apical. Evidence of similar growth is found deeper in 
