169 
The Means of Distribution of Hepaticce. 
Dumortiera irrigua is again met with sparingly in the South- 
West of Ireland near Sore Fell. Since the plants belong to a wide¬ 
spread tropical genus, this fact seems to indicate that they owe 
their present distribution to Miocene and Pliocene times when 
Great Britain and Ireland were united and when the climate 
especially during the earlier Miocene age must have been of a 
tropical character. Unlike Fegatella conicn, Pellia and Aneura, 
which are so constituted as to survive great cold, the greater 
delicacy of Dumortiera irrigua seems to point to the necessity of a 
much higher thermal constant for its perpetuation. The same 
observation would seem to apply to Marchantia polymorpha, Blasia 
pusilla and Lunularia cruciata, which are by no means so evenly and 
widely distributed as is generally supposed. Marchantia polymorpha 
being more hygrophilous than Lunularia cruciata is unable to 
migrate far from the vicinity of running water. The writer has 
never found it growing in situations where the water supply was 
limited to the rainfall, nor in ditches which are intermittently wet 
and dry. Like Metzgeria furcata the male oophyte appears to 
persist to a greater extent than the female, and is more widely 
distributed. The plants grow together in matted groups on the 
shaded side of rocks which form channels for comparatively pure 
water and not far removed from the normal water line so as to be 
ensured against dessication. 
Lunularia cruciata, unlike Marchantia polymorpha, has a wide 
distribution, not being confined exclusively to water courses, but is 
found growing in isolated patches in very diverse situations. The 
writer has found it growing upon boulders occupying deep seated 
valley-beds, upon stiff clay loams forming the banks of roadside 
water channels, at the bottom of old walls and outhouses, and upon 
shaded banks often hidden from view by overhanging brambles. 
This wide distribution of Lunularia cruciata is in no sense due to 
spore dissemination. The sexual activity so far as British repre¬ 
sentatives are concerned has declined to such an extent that the spore¬ 
bearing organs are now only met with in more Southern latitudes. 
Dr. A. Gepp however showed me a specimen of the fully developed 
sporophyte which had been produced by culture in a greenhouse. 
The writer has occasionly met with specimens of the female 
oophyte in which archegonia were present, but never with the 
mature sporophyte bearing spores. Since however the organ has 
been produced under the more even temperature of a green-house 
and is still produced upon plants in more southern latitudes, we 
