i86 
H. W. RICKETT 
those grown in nutrient solution; in these instances the terminal cell 
seemed to function as an apical cell, forming a narrow ribbon composed of 
pairs of cells (figs. 35, 36, PI. X), the whole gradually broadening out into 
a flat plate. In the latter stage, however, the appearance of an apical cell 
was lost, and lateral growing points often appeared, from each of which 
presumably, under favorable conditions, a thallus would have developed 
(fig. 37, PI. XII; text fig. i). 
After the terminal disc has been formed, its further growth usually 
becomes markedly one-sided. This results from the development of a group 
of rapidly dividing initial cells at one side of the disc. This tendency is 
illustrated in figures 15, 17, etc., Plate IX. Division in this group of cells 
takes place in several planes all at right angles to the original divisions of 
the germ tube, so that a flat plate, one cell thick, grows out at right angles 
Text fig. i. An abnormal thallus which resulted from a spore germinated in nutrient 
solution: a, a', a", apical regions; b, basal cell; r, rhizoids. The cell walls at a' could 
not be seen on account of the density of the cell contents. Drawn from living material, 
X about 50. Compare figures 35 and 36, Plate X, and figure 37, Plate XII. 
to the latter. At first the plate is cup-shaped, owing presumably to the 
more rapid growth of the edges; later, however, it spreads out into a flat 
blade. This process is illustrated in figures 17-26, Plates IX and XII. 
It is noteworthy that one of Campbell's figures (3) of a sporeling of Riccia 
bears a strong resemblance to some of these figures, such as figure 23. In 
most cases, growth occurs by the division of a few cells at one point on the 
margin of the plate. Sometimes two such groups of initials may be formed, 
resulting in a marginal growth of the thallus at two points (a, a', figs. 27, 
PI. XII, and 28, PI. X). In the particular case shown in figure 27 there is 
