1914] PICKETT—PROTHALLIUM OF CAMPTOSORUS 231 
or longitudinal plane. In some instances consecutive transverse 
divisions occur until a long, protonema-like filament of many cells 
is formed (figs. 1, 2, 3, 61). The length of the filament may vary, 
but whether it be one cell or more than one cell in length, it finally 
produces, by longitudinal and further transverse divisions of its 
newer cells, a flat plate one cell in thickness. It should be noted 
that it is the rule for this plate to be formed by regular promiscuous 
divisions, without any suggestion of an apical cell or group, although 
exceptions may be found in unusually long filaments. Not infre- 
quently this plate is formed immediately after the first transverse 
division of the spore (figs. 4, 18). In other specimens the plate 
formation begins after a chain of two or more cells is evident 
(figs. 5, 6, 8, 10, 61, 63). Occasionally a prothallium shows that 
transverse divisions have been followed or accompanied by longi- 
tudinal divisions until a strand two cells wide and as long as the 
simple protonemal structure mentioned above has been formed 
(figs. 7, 11, 14). Fig. 13 shows an intermediate form where one 
cell of a single row has given rise to two by longitudinal division. 
More rarely a definite strand three cells in width is clearly shown 
(fig. 19). That these strands, one, two, or three cells in width, are 
hot a part of the regular prothallial plate is indicated by the abrupt 
beginning of the latter (figs. 5, 6, 7, 11, 14). 
Later growth of the prothallia 
The small prothallia increase in size by a promiscuous division 
of their cells in two planes. The location of growing regions and 
the direction of division of individual cells seem to follow no general 
rule. The resulting cell plates lack to a marked degree the regular- 
ity and symmetry usually found in the prothallia of related ferns. 
A glance at figs. 1-20 and at pl. XIII will give an idea of the many 
and various forms found. This continued promiscuous growth and 
division of the cells in the body of the prothallium is characteristic 
of Camptosorus rhizophyllus. In many cases prothallia of con- 
siderable size are formed by this growth alone before the formation 
of an apical region, as must have been true in those shown in figs. 
"319, and 59. This type of growth continues after the appearance 
