40 PROF, JULIUS MACLEOD ON TEN 
PART IV; 
DESCRIPTIVE TABLES OF TEN SPECIES OF THE Genus Mxrua. 
§ 38.—In the present part I give the quantitative description of ten British 
species of the genus Mnium*. For two species (orthorrhynchum, spinosum) 
which are rarely found in fruit in these Islands, it has been impossible to 
obtain fertile British specimens ; therefore I examined specimens from the 
continent, which were kindly given to me by Mr. H. N. Dixon, F.L.S. 
The description of each species includes two Tables, viz. : 
1°. A Table A, in which I give the minimum and maximum values of twelve 
characters of the leaves in the 10th interval (see § 6; $16, Table XIII. A) 
of the fertile stem, and of two more characters (total number of leaves of the 
fertile stem and number of fruits). The limits are obtained by the measure- 
ment of specimens from as many localities as possible. 
Many of the given limits are merely approximate and are very likely to 
be corrected by further measurements. I hope, however, that corrections 
will be rather unimportant, except perhaps for three rare species (affine, 
orthorrhynchum, spinosum), material of which could not be obtained in 
sufficient quantity. As they are, the Tables may give an adequate idea of 
the method. 
2". A Table B, in whieh I give the gradation curves of the twelve 
characters of the leaves. For each species the figures in the ten intervals 
were obtained from specimens of one patch, the curves being mean interval 
curves (see $ T). Therefore the figures have not the significance of exact 
specific figures. Gradation is, indeed, in a certain degree, variable from one 
patch to another. A complete study of this variation would go beyond the 
limits of this paper. As was remarked in $8, the relative values of the 
ordinates of a gradation curve are more important than the absolute values. 
I prefer, however, to give the absolute values, by means of which the relative 
values (percentage curves) may be easily calculated (§ 8)—whilst it is 
impossible to caleulate the absolute values by means of percentage curves. 
On the definition and the measurement of the characters, see Part III. 
ABBREVIATIONS : 1°, Length of the midrib (see § 35) : 
(a) Midrib short (ceasing below the summit of the leaf) : —. 
(6) Nerve longer (a trace of connection between nerve and summit): +. 
(c) Nerve as long as possible (reaching the summit of the leaf): +. 
2°. Tooth at the summit of the leaf : 
(a) Tooth present: +. 
(b) Tooth absent : —. 
* The same method is applicable to other Acrocarpic Mosses. 
