Howe and Underwood : The Genus Riei.la '2*20 



lower cells then divide in the sagittal plane (/. //) 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. F. 13-16 show stages in the subsequent development, 

 /./ being a view of its proximal surface, and /j, /j and 16 of its 

 distal, the point of attachment in each case being at b. The part 

 which is derived from the base of the original trichome con.sists 

 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 suborbicular 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 mcristcmatic ; 

 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. F. 16 shows a well-developed gemma inverted as 

 regards its original relations to the axis of the gametophytc. 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. F. ij shows 

 the outline of a gemma in an older stage, and f. 18 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 /. 21 and /. 

 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 



