II] PROTHALLUS OFTEN IMPERFECTLY KNOWN 51 



classification, and for that purpose therefore they naturally take a subsidiary 

 place. There remain a large number of forms showing a general megaphyl- 

 lous Fern-like habit, with a prevailing uniformity of the external character 

 of the sporophyte. This makes their systematic grouping difficult. It will 

 be necessary to examine them closely, and by exact observation of other 

 details in all stages of their life-history to find features more permanent and 

 therefore more reliable than those of external habit would be. The nature 

 of those characters will be discussed in the following Chapters. 



It may be thought that in this treatment of Habit and Habitat in Ferns 

 the prothallus has been unduly ignored. In the comparisons which are to 

 follow it will take its proper place. But here it must suffice to say that its 

 relative inconspicuousness has led to its being entirely passed over in the 

 ordinary Systematic Works. The fact that the details of the gametophyte 

 are very imperfectly known in the large majority of the species has hitherto 

 made its general use impossible for generic and specific comparison. More- 

 over, the very direct dependence of the prothallus, as regards its form, upon 

 the external conditions ruling during its development is another serious 

 obstacle to its use in comparison with a view to Classification. The com- 

 parative treatment of the prothallus and sexual organs will be reserved till 

 Chapters xiil and XIV. 



BIBLIOGRAPHY FOR CHAPTER II 



13. Engler & Prantl. Natiirl. Pflanzenfam. i, 4. 1902. Here are many illustrations of 

 general habit. 



14. Christ. Geographie der Fame. 1910, where floristic literature is quoted. 



15. Velenovsky. Vergleichende Morphologic der Pflanzen. Prag. 1905. Teil i. 



16. Von Goebel. Organographie. 1918. Teil 11, Heft 11. 



17. Sahni. Tubers of Nephrolepis. New Phyt. xv, p. 73, where literature on storage is 

 quoted. 



18. MclLROY. Proc. Roy. Phil. Soc. Glasgow. 1906. 



19. Boodle. Structure of the leaves of the Bracken. Linn. Journ. xxxv, p. 659. 



20. Karsten. Teratophyllu7n aculeatuin. Ann. Jard. Buit. xii, p. 143. 



21. Christ. Biol. u. Syst. Bedeutung d. Dimorph. bei Epiphyt. Farnpfl. besonders 

 Stenochlaena. Verh. d. Schw. Naturf. Ges. 89th Meeting. July 1906. 



22. Yapp. Two Malayan myrmecophilous Ferns. Ann. of Bot. xvi, p. 185. 

 See also the Floristic works quoted for general use on p. ix. 



4—2 



