56 Mr. W. S. MacrEaY on certain general Laws regulating 
degree must be determinate ; and it only remains for the natu- 
ralist to discover from observation what this number is. 
That Nature has made use of determinate numbers in the con- 
struction of vegetables has long been known empirically ; as for 
instance, where botanists have found the typical number of parts 
of fructification in the acotyledonous plants of Jussieu to be two, 
that in monocotyledonous plants to be three, and that in dico- 
tyledonous plants to be five, or multiples of these numbers. 
Consequently the existence of a determinate number in the dis- 
tribution of the plants themselves might have been argued 
à priori. And in this manner indeed M. Fries appears to have 
argued ; for it is tolerably clear that it was the consideration of 
the foregoing rule, adopted by Nature in the structure of acoty- 
ledonous plants, which induced him theoretically to assume four 
as a multiple of two to be the determinate number in which 
Fungi are grouped*. I say this, because he is obliged from ac- 
tual observation to admit that of these four groups, one is exces- 
sively capacious in comparison with the other three, and is always 
to be divided into two. So that we may either, with M. Fries, 
consider every group of Fungi as divisible into four, of which 
the largest is to be reckoned as two,—a supposition that would 
not only make two determinate numbers, but which, from the 
binary groups not being alway analogous, will moreover break 
the parallelism of corresponding groups,—or we may account 
every group as divisible into five, and thus not only agree with 
M. Fries's observations, but besides keep the parallelism of ana- 
logies uninterrupted. If in this state of the matter it could now 
* [t ought here to be observed, that Ocken had previously advanced the opinion 
that four was the determinate number in natural distribution. 'This naturalist, however, 
having in his Natárgeschichte für schulen, lately published, in a great measure aban- 
doned the number four for five, and that more especially in the animal kingdom, has 
thus got into all the difficulties which necessarily attend the supposition of two determi- 
nate numbers. — 
be 
