VUE BRYOLOGIQUE. 
aie form, i. e. instead of being normal they : remain ovate- 
_ acuminate or cuspidate, the acute apex occupying a much greater 
à proportion of the whole than in the adult leaf, Occasionally there 
may be seen a leaf which has made a further advance, 50 as to be 
almost normally shaped, but its development has there been 
arrested, the only différence from a mature leaf then consisting in 
_ the much smaller size and the cells in the upper half of the leaf 
remaining very small and undeveloped. 
= Thave not found these undeveloped, rudimentary leaves on the 
upright, fertile stems, nor on the erect shoots of var. elatum. I 
have observed them in M. cuspidatum Hedw , but less frequently 
and less clearly differentiated. In M. affine 1 have found them on 
occasion quite numerous, say one Lo every three of the normal 
leaves, but as a rule much fewer, except where the creeping stem 
remains in contact with the ground and rooting, in which case all 
‘the leaves may remain in this. undeveloped condition, i. e. the 
stem is truly stoloniform. 
= These two species appear io mark the first Ésohationary steps in 
the development of the accessory leaves. 
In Mnium rostratum they have reached a further stage.Here the 
young leaves at the growing point will be found to be of a diffe- 
_rent form from those of M. affine, being almost orbicular, not acumi- 
nate, with only a short and often obtuse apiculus. The leaves here, 
100, rapidly increase in size with the growth of the stem, but side 
by side with the normally developing leaves there will generally 
_be detected here and there minute leaves of quite a different 
character, in which there has proceeded a considerable develop- 
ment in tissue, while the growth in size has been entirely arrested. 
The ordinary foliage leaves in juxtaposition, i. e. of about the 
same age, may have attained half their normal dimensions, the 
_median and upper cells being small, highly chlorophyllose and 
entirely different from the narrow, hyaline border cells, which 
_are now Clearly differentiated in several rows; the accessory leaf is 
comparatively minute, — perhaps scarcely wider {han the diameter 
of the stem — the form fixed and constant, viz. suborbicular or 
widely ovate, with an obtuse apiculus ; the cells all more or less 
homogeneous, with firm walls, narrowly rhomboid-hexagonal, 
prosenchymatous, pellucid and without trace of chlorophyll, the 
marginal ones scarcely different except lhat a single row or 
perhaps two may be somewhat rectangular and elongated, so as 
to form an undefined border, resembling that found in some 
funarioid mosses, or in M. cinclidioides. The nerve is always faint, 
somelimes almost obsolete. À well developed sterile stem of 
