140 Johnson . — On the Development of the 
occurrence of the sporocarps on one side of the petiole only, 
and also for their origin by a single apical cell instead of 
a series of marginal cells like the pinnae. 
Growth by the apical cell continues till more than twenty 
pairs of segments are formed. In the primary division of the 
segments one more section is formed dorsal to the marginal 
cell than in the leaf. The epidermis is formed much as in 
the leaf, but the mesophyll and its air-canals are less developed, 
while the hypodermis is of two much-thickened layers. The 
longitudinal bundle (axial in the stalk and dorsal in the 
capsule) is derived from section I only ; the lateral branches 
of this in the capsule are formed in sections III and IV ; 
and the placental bundle and branch from section VI. The 
sporangia of each sorus are all derived from one macro- 
sporangial cell, and two microsporangial cells are formed in 
the basiscopic marginal cell of each soral segment. 
The microsporangia and the macrosporangia are thus 
derived from sister-cells, and the former do not come from 
segments of the apical cell of the latter as described by 
Russow and Biisgen ; neither is the view of these authors 
as to the origin of the placental bundle from these same 
segments the correct one, as was stated a few lines above. 
A stalk-cell, homologous perhaps with that of the other 
Leptosporangiates, is formed in the development of the 
microsporangium, but nothing that could be so interpreted 
was seen in the macrosporangium. 
The soral canals arise by the separation of the primary 
sporangial cells from the outer cells of section V, and are 
entirely external in origin. The indusium surrounding each 
sorus arises by the more rapid growth of the superficial cells 
of the ventral side of the capsule which grow out and close 
together over the ends of the sporangial cells. Its develop- 
ment thus seems to warrant the statement that it is a true 
indusium morphologically as well as physiologically. The 
gelatinizing tissue of the dorsal part of the capsule is 
apparently the equivalent of a part of the vascular tissue 
of the petiole, while that at the ventral edge probably comes 
