272 
F. Cavers. 
though the margin may he slightly toothed. The leaves are at first 
inserted transversely on the stem, and the insertion remains as a 
transverse line when the leaf consists of two or more simple cell- 
rows ( Arachniopsis , Blepharostoiua), but as a rule the insertion line 
becomes shifted so that it runs obliquely across the stem. This 
shifting is due to unequal growth in length of the upper and lower 
portions of the stem tissue. If this growth is liypotropic (greater 
on the lower side), the stem curves upwards, away from the 
substratum, at the growing tip of the shoot, the line of insertion 
Fig. 45. A, Lophocolea bidentata, dorsal view ; B, Scapania nemorosa, dorsal 
view ; C, Radula complanata, dorsal view ; D, Radula, ventral view. Descriptions 
of leaf-insertion, leaf-lobing, and perianth are given in the text. 
