(572 PROFESSOR F. O. BOWER ON 



actual relation of each apparent pair is like that of the lateral lobes already 

 discussed in O. regalis, and the seemingly paired limbs are in each case forkings of 

 different order. In fact, they constitute a -close scorpioid sympodium. 



The point is clearer in the vegetative leaf of Marsilia, a genus now acknowledged 

 to have near affinity to the Schizseacese, which will be considered later. 



In other genera of the Schizseacese the equal dichotomous branching is widely 

 departed from in the direction of sympodial forms. Prantl has analysed the steps 

 towards this condition, both in the adult and in the juvenile leaves of Lygodium 

 circinatum. He remarks* that notwithstanding the complexity of the adult leaf 

 of Lygodium, the underlying architecture is simple. There is a spindle " of 

 unlimited apical growth, which bears alternating " primary segments " : each of the 

 latter has a short secondary spindle, and it bears regularly two secondary segments, 



a b 



Fig. 6 bis, a, b. — Branching in the fertile region 

 of Schizcca dichotoma. (x 4.) 



which vary in character according to the species. They show conditions grading 

 between that of a dichotomy of the venation (shown for L. palmatum in Prantl, 

 pi. i, fig. 1, which is comparable with our fig. 1, d, of the young Osmunda leaf) and 

 the sympodial development with a terminal lobe, having a midrib (in L. venustum, 

 Prantl, pi. i, fig. 9, which is comparable with our fig. 1, g, of an older leaf of 

 Osmunda). In its secondary segments L. circinatum, corresponds essentially with 

 the former type. 



Having ascertained this transition by comparison of the secondary segments in 

 different species, Prantl examined the juvenile leaves of L. circinatum, and found 

 that, in their successive stages from the cotyledon onwards, they as a whole showed 

 just the same transition from the dichotomous to the sympodial type, and he 

 represents them by schematic drawings,"!" which with slight modifications are 

 reproduced as fig. 7, a, b, c. Of these, fig. a represents the condition of the 

 cotyledon, which shows a regular dichotomy. Fig. b shows the state of a later 

 juvenile leaf, in which the shanks are unequally developed and a sympodial state 

 is initiated. Fig. c represents the condition of the adult leaf, the arrow indicating 

 the unlimited growth of the sympodial rachis, upon which the pinnae now take 

 a lateral position, characteristic of the scorpioid sympodium. 



* Schizaeaceen, p. 8. f PI. i, figs. 12-14. 



