126 Johnson . — On the Development of the 
pair of pinnae (p 1 ., Fig. 18). Each pinna is formed from the 
whole length of one segment (usually the lower one) and 
most, but not all, of a second (Fig. 19). In this respect the 
pinnae resemble those of Ceratopteris (Kny 75 ) and differ 
from those of Asptenium serpentini (Sadebeck ’ 73 ) and Onoclea 
(Campbell ’ 87 ), in which the pinnae are equal in extent to the 
segments. 
Soon after the apical growth ceases, the segments beyond 
the first pair of pinnae, except part or all of the one next 
the lower pinna on each side, begin to swell out in a similar 
manner to form the terminal pair of leaflets.' 
In a transverse section of the leaf through the pinnae, which 
is practically the same for both pairs, we see that the swelling 
mentioned is due to the continued activity of the marginal 
cells (Fig. 20). No pericline is formed in these, as in the 
marginal cells of the petiole, but anticlines parallel alternately 
to walls IV, V are formed continually until the pinna is two 
millimeters broad or more (Fig. 2i). The additional sections 
thus formed divide like the earlier ones by periclines to form 
the three meristem-layers of the lamina. The marginal cells 
also divide frequently by anticlines perpendicular to the edge 
of the pinna, thus constantly increasing in number and giving 
the pinna a fan-like shape with rounded outer edge formed 
by the actively dividing marginal cells (Fig. 19), as was shown 
by Hanstein. The pinnae are directed more ventrally than 
laterally from the petiole, and the upper pair soon come to 
have their upper or ventral surfaces nearly in contact, while 
the lower and older pair fold together (Fig. 21) to enclose the 
younger ones between them in the bud (Fig. 25). 
A branch of the axial bundle is given off to each pinna, 
which branches to form the anastomosing veins characteristic 
of Marsitia ; but the exact development of these bundles of 
the pinna was not studied, and I cannot state whether they 
arise, as Sadebeck ( 74 ) has shown them to, in Aspteiiium. 
The epidermal cells of the leaf give rise to stomata on the 
upper or both sides, and to deciduous trichomes like those 
of the petiole. 
