BRITISH SPECIES OF THE GENUS MNIUM. bL 
stem first into 1000 grades. The leaf 1 (lowest leaf) is placed at 0°, the 
leaf 2 at 429 *, .... the leaf 6 at 209°, .... the leaf 25 (the longest 
one) at 1000°. I divide now the part of the stem under consideration 
into ten intervals, viz., interval 1 from 0° to 99°, interval 2 from 100° to 
199°, .... interval 10 from 900° to 1000°. Table III. gives the number of 
leaves in each interval. 
TABLE III. 
A fertile stem of Mnium serratum, Schrad. : number of leaves in the ten 
intervals. Total number =25. Compare Table II. 
Intervals: 1. 9. 3. 2 5. 6. 7. 8. 9. 10. 
Number of leaves.. 8 2 8 2 9 3 2 3 9 8 
I calculate now the mean value of the property length in each interval, 
using the figures given in Table II. See Table IV. 
TABLE IV. 
Interval curve of one fertile stem of Mnium serratum. Mean length of 
the leaves T in 10 intervals, in mm. 
Intervals: 1. 9. ioc 4. 5. 6. the 8. 9. 10. 
Meandonsth. 2.0176 2:10 . 288emibeeee oO. 58:05. 8373 Bal 377. 4:50 
As the curve in Table IV. represents one specimen (fertile stem), I call it 
a specimen interval curve. 
§ 7. MEAN INTERVAL CURVE.—We may, in a similar way, construct the 
mean curve of a given character of a certain number of stems which were 
developed under the same conditions of existence. The safest way is to take 
stems belonging to the same patch. 
Example : I have measured the lengths of all the leaves (114 in number) 
of 11 fertile stems of Mnium punctatum collected by Prof. Barker (Llanberis 
to Bangor, Wales). Table V. gives the number of leaves of each of them in 
each interval (see the method of calculation in $ 6). It must be observed 
that in several stems the number of leaves is smaller than 10 ; even in such 
cases the place of each leaf is calculated by means of the general method 
used in $ 9. 
* 1000: (25—1) = 417. 
T Leaf 1 was damaged and could not be measured (see Table IL.). Therefore only two 
leaves are taken into account in interval 1. ; 
