22 SIR DIETRICH BRANDIS—AN ENUMERATION 
diameter of average pith-cells, while in some species of Shorea 
(section Anthoshorea) they are very small, about the width of 
pith-cells, and consequently not easy to recognize. 
A character not yet mentioned, upon which Heim lays great 
stress, are the sclerotic cells in the cortex. They either have 
their walls uniformly thickened all round (Anisoptera, Vatica, 
Stemonoporus, Vateria), or the wall is thickened on the inner side 
only. Those last named may be designated as horse-shoe or 
C-shaped cells, the thin wall being outside, towards the epidermis 
(Doona, Hopea, Shorea). Both kinds of sclerotic cells are found 
in the cortex of Dryobalanops and some species of Dipterocarpus. 
Anatomical characters are not in themselves more valuable 
than external morphological characters. The progress of scien- 
tific research has not been furthered by the attempt to give 
undue weight to characters drawn from the internal structure of 
plants. Van Tieghem lays stress upon the affinity of Mastixia 
to Dipterocarps, because it has a circle of resin-ducts in the 
medullary sheath; and for similar reasons Van Tieghem and 
Lecomte have suggested that Leitneria should be placed in this. 
order. This means that certain isolated anatomical characters 
are necessarily of paramount importance, and ought therefore to 
override the whole of the external morphological characters upon 
which the present classification of phanogamous plants has been 
based. 
Obviously thisis wrong. All characters must be weighed most 
carefully, whether external or anatomical, with the aim of deter- 
mining which characters in a certain order, genus, or species 
should be regarded as essential; and the art of the systematic 
botanist consists in the judicious selection of those characters 
which are most useful in indicating the affinity of orders, genera, 
and species. As a matter of course, the affinity of different plants 
in reality consists in their entire organization, and not in the 
characters which the systematic botanist selects for purposes of 
classification and description. For these purposes a restricted 
number of characters must necessarily be selected. This selec- 
tion, however, must be based upon the study of the entire 
organization of the plant, its mode of growth, its relation to 
light and shade, and other matters, which may conveniently be 
designated as Biological features. It must, further, be based 
upon the study of its internal structure as well as upon those 
external characters which in phenogamous plants have chiefly 
