44 



while in P. v. pulchevvinum we arrive at a tripinnate form 

 bearing pinnae, pinnules and pinnulets. 



On examining the vein system of such ferns we 

 perceive that the extra development must be due to the 

 simplicity of the vein arrangement. In the normal frond 

 each pinna contains a simple series of forking veins 

 springing from its midrib. Some of these stop short on 

 their way to the edge of the pinna, and form and feed the 

 spore heaps, the rest proceed straight to the margin and 

 terminate there evenly so as to form a regular and smooth 

 edge. In the saw-toothed variety some of these veins 

 push as it were beyond the edge, carrying the tissue with 

 them a little way and thus forming the serrate projections. 

 In the subdivided pinnae this process goes farther, but ff 

 would appear that as soon as the projected parts are so 

 far developed as to require a definite midrib of their own 

 for their support, the pinna-forming tendency asserts 

 itself and further division into pinnules or approaches 

 thereto is the result. In the Cambricum section of this 

 species, the tendency for some of the veins to terminate 

 en route to the margin and form spore heaps is entirely 

 lost, and the vital energy suppressed in this direction is 

 diverted to the formation of extra foliar tissue, the veins 

 continuing to lengthen and fork repeatedly, so that the 

 divisions are greatly lengthened and widened and a very 

 beautiful plumose or feathery type is the result. 



The crispum or frilled Hartstongues owe their develop- 

 ment to a similar diversion of spore producing energyi 

 coupled with the fact that while in the plain flat strap the 

 vein system consists of an even succession of veins, each 

 of which starting singly, herring-bone fashion, from the 

 midrib, almost immediately forks into two, and continues 

 as a pair to the frond edge, in the crispums they fork 

 repeatedly, carrying tissue between them, and as a con- 

 sequence the length of the frond on the edges is very much 

 more than at the midrib and the frilling or folding is the 

 result. In some of the " projectum " varieties of this 



