LIST OF NORFOLK MOSSES. 
563 
inwards like the rungs of a ladder. The tooth therefore when 
viewed by transmitted light and a low power presents the simple 
structure of a yellow strip with regular transverse bars. In 
Ptychostomum it is different. The internal transverse bars are 
connected with one another by a series of irregular partitions, some 
vertical, some oblique, giving the appearance of an irregular net- 
work of lines when the tooth is examined as above. This is 
especially marked in 13. pendulum , and often nearly as distinct in 
II. warneum. In some species however, such as 11. arcticum , the 
irregular connecting lines are much fewer, and may be reduced to 
a single almost vertical connection between each pair of transverse 
bars, down the median line of the tooth. Now in 11. mamillafum 
the teeth are almost entirely free from these connecting partitions, 
so that it appears to belong to the Section Cladodium ; but on 
careful examination a single oblique partition or two may be seen 
here and there between the lowest transverse bars at the very base 
of the tooth. It therefore, as has been said, forms in some degree 
a connecting link between the two sections. 
This structure of the peristome distinguishes 11. mamillatum 
clearly from 11. irameum, which in other respects it resembles more 
closely than any other of our species. In addition to this the leaf 
margin is more strongly recurved than is 11. tcnmeuni, the mouth 
of the capsule wider, the lid llatter, and the cells of the outer layer 
of the capsule wall much less incrassate ; 11. lacustre differs in the 
much smaller spores, the smaller more pointed lid, the less strongly 
bordered leaves, and the inflorescence synoicous, not autoicous. 
11. pendulum differs at once in the peristome, while both it and 
B. inclinatum have more tapering leaves with more excurrent 
nerve, and leaves red at the base. The other allied British, 
species of these two sections (except the high alpine species, 
B. arcticum, 11. purpurascens and 11. lawersianum) are known at 
once by the obtuse or sub-obtuse leaves with nerve ceasing below 
the apex. 
The spores in 11. mamillatum are larger than in any other species 
of Bryum with which I am acquainted. In Bom&nsson’s specimens 
from Aland they measure 40 — 50 p. In the Norfolk plant they 
average 4 Sp, many reach 55^, and a few as much as 62 and 67p. 
Altogether it is a very interesting plant, and a great acquisition to 
our moss flora. 
