. The origin of a land flora, a theory based upon the facts of alternation. Plant morphology. 322 LYCOPODIALES is doubtful what is the evolutionary relation between the distal and the basal insertion of the sporangium upon the sporophyll ; whether the one or the other is the more primitive in the Lycopodiales must be left for the present open, but it is evident that such differences as these are of degree only, in a type which is constant as regards the numerical relation of the sporangia to the sporophylls, and in the coincidence of the median planes of both of those parts. There seems little
. The origin of a land flora, a theory based upon the facts of alternation. Plant morphology. 322 LYCOPODIALES is doubtful what is the evolutionary relation between the distal and the basal insertion of the sporangium upon the sporophyll ; whether the one or the other is the more primitive in the Lycopodiales must be left for the present open, but it is evident that such differences as these are of degree only, in a type which is constant as regards the numerical relation of the sporangia to the sporophylls, and in the coincidence of the median planes of both of those parts. There seems little reason to hold that these peculiarities of Spencerites are archaic relatively to those of the ordinary Lycopodinous type. Comparison does not make it necessary, nor even probable, while stratigraphically the ordinary Lycopod type is quite as early as Spencerites. The same relation of sporangium to sporophyll as is seen in the living Lycopods is maintained in the Lepidodendroid cones, which are. Lefridostrohns Brtrwnii. A radial section traversing the axis, a sporophyll, and a sporangium. In the latter numeious spores are seen partially filling it, while sterile processes project npwards'into the cavity. (From Sowerby's drawing.) known in many cases to bear ligules, and to be heterosporous, thus corresponding more especially to the ligulate series of the Lycopodiales; but this may possibly not be the case for all of them. An examination of the details of the sporangium will naturally be best carried out in the best preserved specimens, though these may not be generally typical of all others. Lepidoslrobus Brownii, Schpr., is probably the best preserved of Lepidodendroid cones, and it will therefore be taken first. The large silicified specimen in the British Museum was first described by Kobert Brown, with drawings by The original specimen was about two inches in length, and of about the same diameter : it was evidently only the upper half of a strobilus, as the inter
Size: 2050px × 1219px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, bookpublisherlondonmacmillanand
