XV] EMBRYOS WITHOUT SUSPENSOR 309 



etidoscopic. Consequently the varying inclination of the archegonium to the 

 vertical necessitated in certain cases a subsequent curvature of the embryo, 

 so as to secure the upward direction of the shoot. The embryos oi BotrycJdiim 

 obliqimrn and Helmintliostachys (Figs. 288. 289), as well as those of various 

 species of Lycopodiuui and Selaginella, illustrate the inconvenient shifts that 

 followed from a polarity controlled, in its relation to the archegonium, by 

 the inherited suspensor. Those of Ophioglosstnn viilgatum, and Botrychiicni 

 Limaria (Figs. 292, 293), as well as oi hoetes, show how the absence of the 

 suspensor has removed the restricting tie, and thus simplified the problem of 

 establishment of the sporeling without such contortions. In the case of the 

 Marattiaceae no curvature \& necessary, but " the suspensor seems to be of 

 no particular use" (Lang). It certainly helps to embed the embryo in the 

 prothallus : but though relatively fleshy the prothallus is a flattened body, 

 and the embryo of Macroglosswn shows how the elongation of the suspensor 

 runs parallel to its surfaces, not vertically inwards (Fig. 287). Its elimination 

 in most of the Marattiaceae seems to have removed a useless vestige. The 

 facts for the Eusporangiate Ferns, and for the Lycopodiales as well, indicate 

 that the suspensor is vestigial : that its survival is intelligible in certain 

 cases, but that its removal has set the embryo free from an unnecessary and 

 inconvenient tie\ 



As in hoetes among the Lycopodiales, or Ophioglossum and Botrychmrn 

 Lunaria among the Ophioglossaceae, so the Leptospor^ngiate Ferns, having 

 no suspensor, are not restricted in the orientation of their embryos rela- 

 tively to the axis of the archegonium. They also are free to adjust the 

 polarity of the embryo, and they have assumed an orientation peculiar to 

 themselves. Throughout the Leptosporangiate Ferns the first segment-wall 

 lies approximately in a plane that includes the axis of the archegonium, 

 instead of transversely to it. This provides for the prone position of the 

 axis. The adjustments of the cotyledon and root are such as to allow their 

 ready protrusion, while the enlarged foot maintains communication with 

 the parent prothallus. The proof of the fitness of these arrangements which 

 follow upon the prone position appears in their constancy in the great series 

 of the Leptosporangiate Ferns. Notwithstanding the loss of the suspensor, 

 which consequently gives a less obviously filamentous form to the young 

 sporophyte, it is still correct to preserve the view of it as a spindle-like body • 

 theoretically and by Descent, with polarity marked by the position of the 



^ No suspensor has been described for Tiiiesipteris. Lawson and Holloway both agree in the state- 

 ment that the shoot-region of the embryo is directed towards the archegonial neck, while a suctorial 

 organ with filamentous outgrowths penetrates into the prothallus. This orientation resembles that in 

 Isoetes, Eqiiist'tuni, Ophioglossiini vulgatuin, and BotrychhiDi Lunaria, which are all types without a 

 suspensor, having the apex directed towards the neck of the archegonium {exoscopic). But the 

 absence of a suspensor is remarkable and rather unexpected in an organism so primitive as Tmesipteris, 

 and especially since its prothallus is relatively massive. 



