. The origin of a land flora, a theory based upon the facts of alternation. Plant morphology. THE SPORANGIUM 637 (Fig. 339), and is still more pronounced in Cystopteris and Lindsaya. Thus the equal lips may be differentiated, the one taking on the structure of the leaf-margin, the other becoming a mere appendage of the surface. There is reason to believe that a reduction of the indusium has taken place along more than one line of descent; one such probable series of reduction may be traced from Cyathea to the very interesting conditions seen in Hemitelia with its one-sided indusium, and in Woo
. The origin of a land flora, a theory based upon the facts of alternation. Plant morphology. THE SPORANGIUM 637 (Fig. 339), and is still more pronounced in Cystopteris and Lindsaya. Thus the equal lips may be differentiated, the one taking on the structure of the leaf-margin, the other becoming a mere appendage of the surface. There is reason to believe that a reduction of the indusium has taken place along more than one line of descent; one such probable series of reduction may be traced from Cyathea to the very interesting conditions seen in Hemitelia with its one-sided indusium, and in Woodsia and Hypoderris, in which there is an exiguous, fimbriated indusium. It is but a slight step from these to some forms of the comprehensive genus Polypodium, in which, with a similarly superficial sorus, the indusium is absent. Another line of possible reduction may be traced from the Dennstaedtiinae, through Hypolepis, to certain types of Polypodium. The probability is that there is here a progression from a type with basipetal succession of sporangia protected with a basal indusium, to a mixed type in which the indusial protection is less essential, and the indusium is accordingly abortive. The Sporangium. The morphological equivalence of the sporangia of Ferns at large will be generally admitted, whatever their modifications of detail may be. It has been customary to distinguish the Leptosporangiate from the Eusporan- giate types, on the basis of the origin respectively from one or from several. Diagrams illustrating the segmentation of Ferns. a = Polypodiaceae (compare .Kny, Wandtafeln XCIV.) b=Ceratofteris (compare Kny, Parkeriaceen Taf. XXV., Fig. 3). c=Alsothila (compare Fig. 334). d=Schizaea, (compare Prantl, Taf. V., Fig. 69), or Thyrsopteris (compare Fig. 329), or Trichomanes (compare Prantl, Taf. V., Fig 92). e,f= Todea (compare Fig. 29s). g= Angiopteris (compare Fig. 284). parent cells. But comparative observation shows that this distinction is based not on any d
Size: 2028px × 1233px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, bookpublisherlondonmacmillanand
