XLI] 



ACROSTICHOID DERIVATIVES 



131 



Plecosorus Fee 

 It seems probable that the small genus Plecosorus, which comprises three 

 Central American species, also finds its best place here. The superficial, 

 apparently non-indusiate sorus, borne on the deeply concave lower surface 

 of the contracted pinnules, together with the chaffy scales and general habit, 

 suggest a highly xerophytic type of Dryopteroid (E. and P. I, 4, Fig. lOi, 

 p. 194). 



Fig. 662. Acrophorus stipellatits (Wall.) Moore. « = sorus in surface view ( x 35). 

 (^ = pinnule showing the veins continued beyond the sori ( x 10). 



ACROSTICHOID Derivatives 



The developmental study of the Acrostichoid state carried out by Frau 

 Eva Schumann {Flora, Bd. 108, 191 5, p. 201) has greatly aided the elucidation 

 of the old composite genus Acrostichiiin, and the distribution of its con- 

 stituents to their several sources of probable origin. A generous share falls 

 to the Dryopteroid source, particularly those Ferns that are associated under 

 the generic name of Polybotrya. The relation of the old genus Menisciwn of 

 Schreber to Dryopteris has been so far recognised as to lead to its inclusion 

 within that genus by Diels, and by C. Christensen. It now appears from 

 comparison with Meniscium that certain species also oi Leptochilns are best 

 regarded as being ex-indusiate derivatives of Dryopteris. 



The absence of an indusium, already seen as a not infrequent feature of 

 Dryopteris, gives a greater freedom for the fusion of sori, and for the spread 

 of the sporangia over the general leaf-surface. Various steps of this may be 

 seen leading to that condition which has been described as "Acrostichoid." 

 A very clear series appears to have had its origin in the section Goniopteris 

 Presl (incl. ]\Icniscinin Schreb.). The old genus Menisciicm comprised tropical 



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