424 Bower . — - Studies in the Phytogeny of the Fiiicales. 
suggestion is no new one. The first statement of such a view that I am 
aware of was pointed out to me by Professor Lang, in the Posthumous 
Papers of Griffith, Calcutta, 1847. On p. 444 of the Journals, Griffith 
wrote : ‘ It would be a curious circumstance if all indusiate Ferns were to 
be found reducible to a marginal production of the reproductive apparatus. 
I will bear this in mind, as certain forms of Pterk or its affinities lead me to 
suspect that in these tribes the indusium may be a long way from the 
margin, and yet be quoad origin marginal. . . . The transition to this might 
reasonably be suspected.’ Again, in Griffith’s Posthumous Papers (Notulae, 
vol. ii, pt. i, p. 600), under the heading Blechnum , he writes : £ The general 
involucre is referable to the indexed margin of the frond, as in Pteris , 
in some species of which the frond is actually produced beyond the inflec- 
tion. We may hence look for any amount of dislocation from the costa, 
forming a very natural passage into Pterisi 1 In no case does an involucre 
not having this origin open internally.’ ‘ It follows hence as a matter of 
course that the intramarginal vein is far within the margin. Thus a section 
will be formed, characterized by the prolongation of the margin of the frond 
beyond the vein to which they belong, Blechnum , Doodia , W oodwar dial 
Considering the . time when these passages were written they are most 
striking, for not only do they adumbrate a view now supported by a wide 
area of developmental observation, but they anticipate in a most remarkable 
fashion the evolutionary aspect of such matters. 
A second suggestion of the same nature, but based upon developmental 
evidence, was made by Burck, in his work Indusium der Varens, Haarlem, 
1874. He recognized the indusium as truly the foliar margin, which had 
curved downwards, while the ‘ flange ’ resulted from intercalary cell-division 
from the convex surface. 
But the most important observations bearing on this question of 
a ‘ phyletic slide ’, and the formation of a new margin to the leaf, are those 
made by Prantl in his memoir, Die Schizaeaceen, 1881. They provide 
an analogy only, as the Schizaeaceae are not nearly related to the Blechnoid 
Ferns. Prantl there demonstrated (pp. 39-46) that in all of the Schizaea- 
ceae the sporangia spring from marginal cells of the fertile segment, but 
that in many of them, and especially in Aneimia and Mohria , the originally 
marginal sporangia are subsequently pushed to the lower surface by unequal 
growth of the tissues below them. This is illustrated very clearly in his 
PI. VIII, Figs. 1 29- 1 40, for Mohria. Below the sporangia which originate 
from single marginal cells, a new formation, showing a marginal segmenta- 
tion like that of the leaf itself, appears on the adaxial side, which grows into 
a flap styled by Prantl an f indusium ’. It appears to take up the function 
and to continue the marginal growth of the leaf in the same way as the 
‘ flange ’ does in Blechnum. Moreover, the vascular strands do not stop 
short at the insertion of the sporangia in Mohria , but extend slightly 
