140 
DR JOHN M‘LEAN THOMPSON ON 
and instead of being raised upon conical emergences, or projecting freely from the 
surface of the stem, they frequently arise from single epidermal cells, are closely 
pressed to the stem surface, and generally point downwards. A few of these 
irregular forms are illustrated in text-fig. 11. They may be considered transitional 
between the more elaborate of the small appendages and the freely projecting 
lanceolate scales. 
It is impossible to determine from dead materials the functions fulfilled by these 
various dermal appendages, but it is generally assumed that hairs and scales act 
chiefly as protections for the growing stem, by providing a mechanical safeguard, 
a zone of dead air, or an excretion of mucilage in which the growing parts are 
bathed. It seems reasonable to assume that some or all of these protections are 
necessary to so xerophilous a plant as Stromatopteris. 
But while the possession of both simple hairs and scales of an advanced type is 
interesting, attention is chiefly centred on the intermediate types of dermal append- 
ages. From a developmental standpoint these may be regarded as forms transitional 
between the simple hairs and the erect lanceolate scales, and as showing a combina- 
tion of characters. But it is noteworthy that neither the simple hairs nor the 
irregular and straight scales possess cells with pitted outer walls, whereas the 
columnar and dome-shaped appendages are almost invariably provided with super- 
ficially pitted cells, and similar cells are common upon the general surface of the 
stem. These latter appendages are common on the lower parts of the axes, and, 
while they may be structures of a glandular excretory nature, they are also open to 
