Purple Cliff-Brake 59 
incipient basal primary pinne. In Fig. 6 they are shown fully 
separated from the part of the blade above them. In later leaves 
additional pairs of primary pinne are formed, and in time a 
series of secondary pinne (Pls. IX, X). 
Each pinna becomes distinct from the part of the leaf beyond 
it before its subdivision into segments, if occurring, is begun, and 
nearly always before formation of any pinna beyond it is begun: 
before or during the formation of the incision that renders the 
pinna distinct from the part of the leaf beyond it, the part of the 
leaf that is to form the pinna usually elongates in the direction that 
the pinna’s apex is to take. Asa result, at any stage of the leaf’s 
development each of the leaf’s ultimate divisions or apical sections, 
excepting the microscopic irregularity of the margins, either with 
rare exceptions is entire (Pl. X, a), or has merely a single, often 
extended, lobe at base on one or each side (PI. XI, a), from which 
it is sometimes partly separated by an incision (Pl. X, c). 
The venation is pinnate. The blade’s primary midvein is so 
little developed in the earliest form of the blade that the venation 
at this stage of development may be called pseudo-flabellate, but 
this midvein becomes evident while the blade is still simple. 
A midvein is evident in all but occasional, very small, newly 
formed, ultimate divisions of the later leaves. The two basal 
primary branches of each midvein are usually much more com- 
plex than the others. In the lobed leaf-sections one or each of 
the two constitutes the venation of a lobe, according to whether 
there is a lobe on one or on each side of the section. The develop- 
ment of the branch into a midvein in the lobe is evident either 
before or, if the lobe be very small, soon after the lobe has become 
distinct from the leaf-section, and in any case before the lobe, as 
a distinct pinna, becomes, if ever, lobed. 
