32 PROF. JULIUS MACLEOD ON TEN 
It may be recommended to the biologist who wants to apply the quanti- 
tative method to exercise himself, by measuring some exactly known 
properties of inorganic objects *. 
In the present Part I give the definition of all the characters I have 
measured, the methods of measurement, and the possible error of the figures 
obtained. 
N.B.—In all the calculations the decimal 0°5 has been taken as 1. 
(Example : 31:5 is brought into account as 38.) 
22, FERTILE stem.—I call fertile stem a stem which bears a ripe or 
almost ripe fruit, or at least a fruit sufficiently advanced in its development 
to make it certain that the leaves, even those which are iuserted near the 
summit, are adult. Here there is no difficulty. 
$33. DEFINITION OF THE WORD “ LEAF." NUMBER OF LEAVES.— The lowest 
phyllomes of a fertile stem often differ in their facies from the true leaves 
which are inserted higher up: therefore they are sometimes called scales 
(for instance, in M. hornum). Asa gradual transition exists between scales 
and leaves, it is impossible to find a strict limit between both: therefore I 
call them all leaves T. 
On the other hand, near the summit of the stem, we find almost always 
some phyllomes which constitute a sort of perianth. Sometimes there is a 
distinct breach of continuity in the gradation between the upper leaf and the 
first phyllome of the perianth, the latter being, for instance, much smaller 
than the former : in such cases, no doubt exists about the limit between the 
true leaves and the perianth. But ordinarily the gradation between both is 
continuous, and we must come to an agreement as to where the limit is to 
be made. 
Proceeding towards the summit (and neglecting the lowest leaves) we 
find: 1°, a certain number of leaves which belong (according to the species) 
to the forms represented in fig. 4, 7, 2, 3 (in 7 the breadth increases from 
the base b to D, and decreases further to the summit of the leaf; in 2 the 
breadth increases from b to B'and is constant between D' and D : in 3 the 
breadth is constant between 6 and B); 2°, approaching the summit we very 
often find the form 4 (narrowed between b and B); 5°, near the summit we 
find ordinarily phyllomes, the breadth of which is decreasing continuously 
from b to the summit without constriction. I give the name of leaves to the 
* For instance: the angles of a crystal, the density of a substance, the boiling-point of 
a liquid, ete. 
+ The differences and also the transition between scales and leaves find their accurate 
expression in the successive figures of the gradation curves (for instance, with reference to 
length, breadth, number of teeth, dimensions of the cells, etc.). 
