346 ORGANOGRAPHIC COMPARISONS [CH. 



absence of a suspensor and the exoscopic orientation of the embryo in 

 Eqiusetum and Tmesipteris (see p. 309). It is possible that in these primitive 

 plants the abortion of the basal pole of the spindle happened early, thus 

 giving the recognised advantage of freedom from the inconvenient tie of 

 the suspensor : and that this was followed by exoscopic orientation of the 

 spindle in accordance with their horizontal or upward-turned archegonia. 

 But on this point the facts do not suffice for a decided opinion. On the 

 other hand the embryology of Seed-Plants, both Gymnosperms and Angio- 

 sperms, accords well with that of the primitive Filicales and Lycopodiales 

 in having the filamentous suspensor as a very constant feature, which serves 

 only an embryonic function and develops no further. Passing to the Bryo- 

 phytes, the hypothesis is in harmony with their embryology, for the sporo- 

 gonium itself is a simple primitive spindle without appendicular organs. But 

 the embryos of Bryophytes differ in the fact that their orientation is con- 

 stantly exoscopic, while in the Filicales and Lycopodiales it is primarily 

 endoscopic. Finally, the primitive spindle with its single row of cells at the 

 base is believed to find its true correlative in that filamentous structure 

 which commonly results from the germination of the spores of benthic Algae. 

 Such comparisons as these appear to place the morphology of the sporophyte 

 of Ferns in its natural relation to that of other great sections of the Vegetable 

 Kingdom. They throw some welcome light upon the general architecture of 

 the Plant-Body, and point in the direction of a filamentous origin for even 

 the most complex sporophytes. 



BIBLIOGRAPHY FOR CHAPTER XVII 



303. Bower. Comp. Morph. of the Leaf in Vascular Cryptogams and Gymnosperms. 

 Phil. Trans. 1884. Part n, p. 565. 



304. POTONIE. Lehrbuch der Pfianzen-palaeontologie. Berlin. 1899. 



305. LiGNiER. Bull. Soc. Linn, de Normandie. Serie 5. Vol. 7. Caen. 1903, p. 93. 



306. SCHENCK. Ueber die Phyl. der Archegoniaten. Engler's Bot. Jahrb. xlii, Leipzig. 

 1908. 



307. Tansley. Lectures on the Evolution of the Filicinean Vascular System. Lecture 1. 

 New Phyt. Reprints, No. 2. 1908. 



308. LiGNiER. Bull. Soc. Bot. de France. I9ii,p. 87. 



309. PoTONiE. Eine neue Pflanzenmorphologie. Naturwiss. Wochenblatt. Juni. 1912. 



310. Lang. Y^mhryo oi Heh?unihosiackys. Ann. of Bot. xxviii, 1914, p. 19. 



311. Lang. Presidential x^ddress to Sec. K. Report Brit. Assn. Manchester. 1915. 



312. Lawson. The prothallus of Tmesipteris. Trans. Roy. Soc. Edin. Vol. 51, Part ni, 

 p. 785. 1917. 



313. Hollow AY. The prothallus and young plant of T'wt'j-^/^/fr/^. Trans. New Zeal. Inst. 

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314. HOLLOWAY. Further Studies on 7;«£'j'//^/£';7>. Trans. New Zeal. Inst. Vol. 53. 1921. 



315. Church. Thalassiophyta. Oxford Press. 1919. 



