688 



PROFESSOR F. O. BOWER ON 



dichotomy of the main veins and fine reticulation from the first (fig. 21, a, b, c, d). 

 The webbing is also pronounced, but variable in the older stages leading to 

 the adult leaf.* 



d 



Fit?. 20, a-d. — Juvenile leaves of Dipteris Lobbiana. a, b, from specimens belonging to Dr Lang ; c, d, after 

 drawings by Miss de Bkuyn. (a, b, c, x 2 ; d, x 2.) 



a b 



Flu. 21, a-.l. — Juvenile leaves of Dipteris conjwjala. (x 6.) 



In the adult leaf of D. conjugata the dichotomy shows a distinctly sympodial 

 tendency. The inner anadromic branches are favoured, as compared with the outer. 

 This is apparent from Plate-fig. B. The same method, without the webbing, under- 

 lies the construction of the leaf of the probably related fossil, Dictyophyllum exile 



* Skward, I.e., pi. xlviii. 



