Cape Species of Passer ina, with some Notes on their Anatomy. 599 
laeaceae. They represent, therefore, in all probability, a more generalized 
ancestral type, the ericoid adult leaf being highly specialized. 
The transition from juvenile to adult leaves is often remarkably sharp, 
at one node typical juvenile leaves being borne, at the next typical adult 
leaves. Occasionally, however, transitional forms are found, with a few 
woolly hairs towards the tip, which is more involute than in the normal 
juvenile leaf. But in such cases the stomata, so far as I have observed, are 
still of the sunk type. The transition is, on the other hand, more often 
gradual in respect of mucilage. The first adult leaves have a number of 
epidermal cells on the outer flanks with thick mucilaginous inner walls, and 
cells may be found here and there in leaves much higher on the young 
plant which still show the same feature. The transition is also gradual in 
the degree of development of fibres. The upper juvenile leaves show the 
characteristic hypodermal sheath of fibres spreading laterally from the veins, 
and the palisade layer is interrupted at the midrib as well as at the two 
chief lateral veins. 
In reference to the gelatinous contents of the epidermal cells of the 
Fig. 13. Dead cells from epidermis of juvenile leaf, showing swelling of mucilage and collapse 
of lumen. Cuticle and brown contents shaded. 
adult leaf, it has been suggested that one advantage lies in the hindrance 
offered to complete collapse of the cells, if, as sometimes happens in the 
older leaves, they die prematurely. The mucilage in the epidermis of older 
juvenile leaves has still more conspicuously a similar action. In dead cells 
the mucilage swells till it occupies nearly the whole volume of the cell and 
compresses the lumen with its brown contents into a very small space at the 
top of the cell (Fig. 13). 
Juvenile leaves in P. cf. falcifolia. Seedlings of this form I have 
seldom found. The lower juvenile leaves are very similar to those of 
P. filiformis, but agree with the adult leaves of the species in having 
a continuous palisade tissue. Fibres are in fact feebly developed. The 
number of examples seen is too few for safe generalization, but the mesophyll 
suggests a shade leaf, with the palisade tissue less strongly developed and 
the spongy tissue more lacunar than in P. filiformis. Other observations 
of a preliminary nature on the distribution of the two species also point to 
P. cf. falcifolia being a species relatively tolerant of shade, whereas P. fili - 
formis grows best in the open, fully exposed to the sun 
