THE LEAF-TRACE IN SOME PINNATE LEAVES. 
15 
we have already seen that the main controlling factors are the length of the leaf and 
the size of the pinnae. 
In close dependence upon this qualifying generalisation there has been established 
a striking parallelism between the grouping of Ferns according to the types of 
pinna-trace found in them and that adopted by Christensen in the Index Filicum. 
A convincing example of this is connected with the genera Aspidium and 
Polystichum. These are generally admitted difficult of delimitation and definition. 
But such Ferns as Nephrodium macropliyllum, Baker (with marginal pinna-trace), 
on the one hand, and Aspidium capense, Willd. (extramarginal), and Aspidium 
falcatum , Sw. (extramarginal), on the other, differ altogether in the features of 
leaf-trace and pinna-trace from Nephrodium Filix-mas, Rich, (extramarginal), and 
Aspidium polymorphum, Wall, (marginal), yet fall at once into line with the 
other species of their genera when named, as Christensen names them, Aspidium 
martinicense, Spr., Polystichum adiantiforme (Forst.) J. Sm., and Polystichum 
falcatum (L. fil.) Diels. 
The case of Microlepia hirsuta (J. Sm.) Pr., referred to above, provides one 
of the few exceptions to the rule that the species of any genus of Ferns in the 
Index Filicum have all the same type of pinna-trace. And a note by Professor 
Bower (Gwynne-Vaughan, ’ 03 , p. 732 ) refers to the divergence of this plant from 
the type of Microlepia ; it is one of the Mixtee ! 
Thus it should be worth while for a systematist, when working with critical 
groups of Ferns, to pay some attention to the forms of leaf-trace and pinna-trace. 
In the Ferns the portion of the pinna-trace derived from the adaxial part of 
the leaf-trace is always nipped off, for the basal and lower pinnee, in the same way 
within a genus * irrespective of the habitat of the Fern. The outline of the leaf- 
trace is constant within a species, though the degree of elaboration of the abaxial 
part of the leaf-trace is directly dependent on the length of the leaf and on the 
size and number of the pinnae. The abaxial portion of the leaf-trace in “broken” 
leaf- traces is employed to reinforce the adaxial strands between the pinnae, and, 
where the pinnae are large, directly to give them a series of strands additional to 
that derived from the adaxial strand of the leaf-trace. 
The Leaf-Traces and Pinna-Traces of the Cycads. 
The anatomy of the leaf in the Cycads has been the subject of numerous papers 
(Yon Mohl, ’ 32 ; Mettenius, # ’61 ; Kraus, ’ 65 ; Bertrand and Renault, ’ 87 ; 
Nestler, ’95 ; Carano, ’03 ; Matte, ’03 and ’04 ; Worsdell, ’06 ; South and 
Compton, ’08 ; Thiessen, ’08 ; Pavolini, ’09 ; Coulter and Chamberlain, TO ; 
Le Goc, ’ 14 ; and Marsh, ’ 14 ). Nestler, Matte, and Pavolini give detailed 
accounts of the arrangements of the strands in the leaf-traces of many genera and 
species, and follow the courses of the strands throughout the leaves ; but the majority 
* Recognised as such by Christensen in the Index Filicum . 
