Cavers: Notes on Yorkshire Bryophytes. 14 
ments in spiral succession, the apical cell growing in size after 
each segment is cut off by a wall parallel with one of the sides. 
In each lateral (more strictly dorso-lateral) segment there 
first appears a wall dividing the segment into an upper and 
a lower cell, the latter being the larger; then the lower cell 
divides by a curved wall cvtting off an inner cell which con- 
tributes to the formation of the stem, while the two outer cells 
of the segment give rise to a sideleaf. In each of the ventral 
segments, the first division separates an inner cell, which con- 
tributes to the stem, from an outer cell which produces an 
underleaf, and which divides by a vertical wall. In each case, 
therefore, the young leaf begins its growth with two cells placed 
side by side around the stem. At first these two cells grow 
out independently, their independent growth lasting for a short 
or long time in different cases, and it is to differences in this 
respect and in the mode of growth of the two primary leaf-lobes 
that the immense variety of leaf-forms in the foliose liverworts 
is due. The later growth of the leaf takes place at the base, 
near the stem, the oldest cells being therefore at the apex and 
margin. In the underleaf the two lobes become triangular, and 
after a time grow together at the base, and grow at about an 
equal rate, but in the side leaf the upper lobe soon outstrips the 
lower and becomes much larger, bending over the growing 
point; all the leaf-lobes bear a club-shaped gland-hair at the 
tip, and sometimes also at the margin and the base, secreting 
mucilage which keeps the growing point moist. The lower 
cell of the lateral leaf (two-celled stage) usually divides at first 
into two, and the cell nearest the stem forms the ‘stylus’ which 
is also tipped by a mucilage hair but undergoes little develop- 
ment. The rest of this lower half-segment then grows out 
to form a rounded or oval plate, and after a time its growth 
becomes restricted to the middle, so that it gradually becomes 
hollow and eventually forms a pitcher. 
When /rullanza plants are grown in air saturated by moisture, 
é.g., by keeping pieces of bark with: /. dlatata, or rock with 
f. tamarisct, in a covered glass dish and watering liberally, the 
new branches are found to bear, instead of pitchers, flat rounded 
or triangular lobules (Fig. 3). In this connexion it is interesting 
to compare with Frullania the closely allied genus /wbula, in 
which the plants are dark green in colour and more delicate 
in texture than in Frudlania (Fig. 4). Lett * gives the habitat 
* *Hepatics of the British Islands,’ 1902, p. 54. 
1907 January I. 
