676 PROFESSOR F. O. BOWER ON 



not exactly opposite : in the drawing the right-hand pinna is lower than the left. 

 The two distal pinnae are an obvious result of bifurcation. Thus, following the 

 adult vascular connections, the whole is to be interpreted as a scorpioid sympodium 

 with only three forkings, and it may be represented diagrammatically as in fig. 9, b. 

 Transverse sections of the mature region of insertion support this conclusion.* The 

 fertile region in Schizsea has been seen to be constructed on the same plan, but 

 carried further by repeated forkings. 



The fertile leaf of M. polycarpa bears a large number of sporocarps, and ac- 

 cordingly offers opportunity for study of their morphological relations. Goebel has 

 shown that in origin these are of the nature of pinnse,f and Miss Allison J has 

 demonstrated that the insertion of their vascular supply upon that of the leaf-stalk 

 is marginal, as are all the pinna-traces in the Schizseace8e.§ The actual origin of 

 the sporocarps as described by Goebel is monopodial. Phyletically the probable 

 explanation of their peculiar arrangement is that in repeated forkings the shanks 

 successively right and left of the forkings are constantly the weaker ; in fact, it is 

 a helicoid sympodium, examples of which will be described below for Matonia and 

 Pteris semipinnata, etc.|| 



The simple acicular juvenile leaves of Marsilia correspond on the one hand to 

 the simple leaves of Pilularia, and on the other to the vegetative leaves of Schizsea 

 rupestris and other species. In all of these it may be held that dichotomy was 

 probably present in the ancestry, as it is in the rest of the Schizseacese. They may 

 be held to have reverted to a condition where the simple juvenile leaf is maintained 

 throughout life. The same may also be the true interpretation of the simple leaf- 

 structure seen throughout life in Salvinia and Azolla. 



*& j 



Marattiacese. 



In Dansea, Marattia, and Angiopteris the ultimate venation of the adult leaf 

 shows prevalent dichotomy. But in Kaulfussia the venation is reticulate. All 

 of them have prominent midribs, from which, in the former cases, the dichotomising 

 veins spring, while each strand extends in Angiopteris and Marattia into a short 

 marginal tooth. The juvenile leaves have been figured in all the genera, but the 

 transitions to the mature state have not been fully followed. Thus Campbell has 

 depicted the juvenile leaves of Dansea,^ of Marattia ,** of Angiopteris, \\ and of Kaul- 



* Allison, New Phyt., vol. x, pi. iii. t Organography, Engl, ed., ii, p. 479. J L.c, p. 204. 



§ Davie, Trans. Roy. Soc. Edin., vol. 1, pt. ii, No. 11, p. 354. 



|| The use of this term is that adopted by Hofmeister, after Bravais (Allg. Morph., p. 435), as applied to 

 monopodial branchings, and transferred to dichotomies also. An inversion of the use of the terms "helicoid" and 

 "scorpioid" appeared both in the Textbook of Sachs, Engl, ed., 1875, p. 157, and in that of Van Tieghem, p. 38. 

 But they are used in their original sense in the Textbook of Strasburger. 



IT Eusp. Ferns, fig. 125, p. 148. 



** L.c, fig. 122, p. 147. 



tt L.c, fig. 122, p. 147 ; also Farmer, Ann. of Hot., vi, pi. xv. 



