Cavers: Notes on Yorkshire Bryophytes. 15 
walls of the cells bear very thin places, or pits, through which 
dissolved substances can pass more readily. The degree of 
wall-thickening and of coloration depends largely on the habitat 
of the plant, especially as regards light, the thickest and most 
deeply coloured cell walls being found in plants growing in the 
most exposed places. From the results of cultures, | have found 
that in Frud/ania and various other liverworts the thickness of 
the cell walls is largly influenced by the amount of moisture in 
the surroundings, while their coloration depends solely on the 
intensity of the light. Cutin is not developed on any part of 
the plant (except on the outer surface of the capsule and in the 
outer coat of the spores), hence water can be absorbed at all 
parts, and is stored during drought, not only in the pitchers and 
in the cavities of the leaf cells, but also in the thick cell walls. 
Plants kept constantly moist not only dispense with. pitchers, 
but also with thickened cell walls. The coloration of the walls 
may act as a screen against too strong light, or may be a pro- 
tection against cold in addition. Experiments have shown * 
that in plants of /. ¢amariscz with deep coloration the gaseous 
exchanges concerned in assimilation and respiration are less 
active than in green plants of the same species. 
Each branch of the stem arises just behind one of the side 
leaves. According to Leitgeb, t the whole of the lower half of 
a segment is used up to form the growing point of the branch 
(Fig. 2), so that the leaf behind which the branch arises has no 
lobule. This is usually the case in /. dlatata and F. tamarzsct, 
which Leitgeb investigated, but from sections and cleared 
apices of several other species of /yw//anza, | am inclined to 
believe that in some cases, at any rate, the branch represents only 
the posterior part of the half segment, and that what appears to be 
the first underleaf of the branch is really the lobule and stylus 
derived from the rest-of the half segment; this would agree 
with the interpretation of the branching in /rud/ania suggested 
by Spruce and by Evans. 
All the British species of Frud/ania are dioecious, though 
fF. dilatata is said to have the male and female branches some- 
times on the same plant. In this species, as was noted by 
Hofmeister, | the male plants usually occur at a higher level on 
the substratum than the female plants, to which the anthe- 
rozoids are washed down by rain or dew, thus reaching the 
* Jonsson, Comptes rendus, 1894. 
+ Untersuchungen tiber die Lebermoose, Heft 2, pp. 22, 25. 
+ Vergleichende Untersuchungen, p. 37- 
1907 January 1. 
