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Pteridophytes . Are they vestigial? 
in fact that here again potential fertility is more extensive 
than that which is realized. At least those leaves which bear 
undeveloped rudiments may be designated sterile sporophylls, 
and the imperfect spikes are to be regarded as vestigial, each 
being subtended not by imperfect, but by a fully developed 
sterile lamina h 
Filicineae. 
In the larger leaved Pteridophyta examples of incompletely 
developed sporangia or sori are not uncommonly met with ; 
but owing to their being distributed over the large leaf-area 
they are less susceptible of theoretical treatment than in the 
simpler cases of the smaller-leaved forms. Many instances 
of transition from sterile to fertile leaves, or parts of leaves, 
in Ferns have been described ; the balance of vegetative and 
reproductive regions, even on the individual leaf, shows some 
interesting analogies with that on the whole plant in some 
species of Lycopodium . Gluck 2 has brought together a large 
number of such cases, intermediate between sterile and fertile 
leaves, which are so far interesting as they show the intimate 
relation of sterile and fertile leaves ; developmentally it hardly 
needs to be reiterated that foliage leaves and sporophylls of 
Ferns are alike ; the two types of leaf are merely variants 
of the same category of parts. Nor does it require to be 
stated again at the present day that in the individual the 
foliage leaves commonly precede the sporophylls. All 
the facts stated by Gluck may be accepted as consistent with 
either the view that sporophylls are phylogenetically ‘ modified ’ 
foliage leaves, or that foliage leaves are sterile sporophylls. 
Stripped of all accessories, his conclusion, that all sporophylls 
are altered foliage leaves, is founded on the assumption that 
the development of the individual is a correct index of the 
evolution of the race, quite irrespective of the results of 
comparison. He arrives at an obvious ontogenetic conclusion, 
and states it as a phylogenetic truth. 
1 Dr. Lang informs me that abortive fertile spikes are commonly found also in 
Helminthostachys , subtended in each case by a fully developed sterile lamina. 
2 Flora, 1895, Heft 2, pp. 322-355. 
S 
