1915] HOLDEN—CUTICLES OF CONIFERS 217 
fixed. Such is undoubtedly the case with cycads; for example, 
Puillophylium hirsutum (29) from Marske is identical both with 
specimens from Whitby in the Sedgwick Museum, Cambridge, 
England, and with others collected by the writer from Navidale, 
Sutherland, Scotland. Since there is such specific constancy in the 
cycads, it is probable that the same holds true for the conifers, 
although too little work has been done on the latter to speak 
dogmatically. 
On the other hand, so far as uniformity within large groups is 
concerned, there seems to be less in the case of the conifers than in 
the cycads. To illustrate: the Bennettitales group may be marked 
off from the Nillsoniales by the sinuous-walled epidermal cells of the 
former as contrasted with the straight walls of the latter; while 
within the Abietineae, sinuous walls have been observed only in 
some species of Abies and Kefeleeria; in the Taxodineae, only 
Cunninghamia; in the Podocarpineae, Saxegothea and Podocarpus; 
and in the Araucarineae, Araucaria. Furthermore, this tendency 
toward diversity even within a single genus is much more marked 
among the conifers than among the cycads. Thus, Dictyozamites 
Johnstrupi Nath. (18) from Bornholm is substantially like D. 
Hawelli Seward (23) from Marske, and the three species of 
Ptillophyllum (P. hirsutum from Yorkshire and Sutherland, P. 
pecten from Yorkshire, and P. acutifolium from India) are very 
similar, both in the sinuous walls and in arrangement of stomata. 
Within the genus Araucaria, on the other hand, members of 
§ Cotympea have the long axis of all the stomata parallel to 
the leaf margin, while in § Euracta there is no uniform angle; 
or even in § Eutacta, A. Cunninghami has distinctly sinuous- 
walled epidermal cells, while in A. Cookii and A. elegans they 
are straight. A similar state of affairs exists for the genus Podo- 
carpus, where within § Evpopocarpus, P. macrophylla and P. 
totara have sinuous walls, whereas in P. alpina and P. elatus they 
are straight. 
Another feature which seems to be fairly constant is the presence 
of characteristic thickenings of the cuticle, either on the accessory 
cells of the stomata or on those of the general epidermis. These may 
constitute teeth projecting into the cavity of the stomatal opening, 
