220 . Howe AND UNDERWOOD: THE GENUS RIELLA 
lower cells then divide in the sagittal plane (/ zz) and this 
this is followed by a division of the terminal cell. The basal cells 
afterward grow out and divide in such a way as to give the body 
a free margin throughout its periphery, though it remains attached 
to the axis for a considerable time by a single cell on its proximal 
surface. /. 13-16 show stages in the subsequent development, 
14 being a view of its proximal surface, and 73, 75 and 76 of its 
distal, the point of attachment in each case being at 6. The part 
which is derived from the base of the original trichome consists 
soon of cells which are smaller, richer in protoplasm, and capable 
of more rapid division than those of the part which is derived 
from the apex of the original trichome. This part of basal origin 
is more regularly suborbieular in outline than the other. In 
neither part can an apical cell be pointed out with any certainty. 
In the earlier stages the whole body seems to be meristematic ; 
later a constriction appears near its middle and the formation of 
new cells is then the most active in the zone of this constriction. 
The larger-celled part, derived from the apex or distal end of the 
initial trichome, becomes at about this time more than one cell 
thick in its middle and terminal regions and shows papilliform out- 
growths, the beginnings of the root-hairs. The smaller-celled 
portion derived from the base or proximal end of the initial tri- 
chome remains only one cell thick except in the isthmus of con- 
striction where it finally, in part at least, becomes two or more 
cells thick. /#. z6 shows a well-developed gemma inverted as 
regards its original relations to the axis of the gametophyte. The 
edges of the two parts here overlap slightly in the zone of con- 
striction. Later, the isthmus elongates, giving the body a some- 
what panduriform or at length subspatulate outline. /. 77 shows 
the outline of a gemma in an older stage, and f. 78 a still later 
development. 
Attempts to germinate the spores of the plants collected by 
Earle and Tracy were made in the autumn and winter of 1902-03. 
Though the spores were to all appearances mature, the attempts 
were successful in the case of only a very few spores, which were 
carried a little beyond the stage represented in our f. 27 and f. 
22. The germ-tubes in every case observed came out from near 
the middle of the outer or more spiny face. This tube is first 
a 
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