50 Anatomie. 



the trace in the Osmundaceous leaf is that found in tbe supply of 

 the smaller veins from the mid-rib of smaller, secondary pinnae; in 

 such cases the trace, whether a band or a crescent, is too small to 

 exhibit peculiar features. In slightly larger traces, the parent Strand 

 of which is a relatively stout C-shaped structure the end of the 

 mother Strand becomes thickened on the side on which the trace 

 is about to depart. The protoxylem on this side elongates so as to 

 become immersed in the thickened extremity of the Strand; the 

 xylem adaxial to the protoxylem may be considered as centripetal. 

 After the later division of the elongated protoxylem the inner of 

 the two protoxylems thus produced is endarch in positions, but the 

 outer, departing one is immersed and therefore mesarch in position. 



In some of the more advanced forms of branching the thickened 

 portion of the parent Strand, the Upper part of which passes out 

 higher up, contains some parenchymatous tissue, xylem-sheath only 

 or xylem-sheath, phloem and pericycle. In such cases a small iso- 

 lated, adaxial mass of xylem, clearly representing the centripetal 

 xylem of the simpler method of branching, is left at the departure 

 of the trace. This detached group of xylem, sometimes reduced to 

 one or two elements, joins up with the main Strand, usually in 

 such a way that the latter remains endarch, but occasionally in 

 front of it, in which case the xylem is temporarily mesarch. A yet 

 further development of this type of branching occurs at the depar- 

 ture of larger traces and results in the production of gaps in the 

 parent trace, the endodermis of which is interrupted so that the 

 ground-tissue of the trace becomes continuous with the external 

 ground tissue, 



The author concludes that there are three distinct regions in 

 the C-shaped Osmundaceous trace: a) the abaxial curve; b) the 

 lateral portion which passes out into the branch trace; and c) the 

 xylem that remains in the parent trace. adaxially to that which has 

 passed out into the daughter trace; phylogenetically this is held to 

 represent the centripetal xylem of the adaxial portion of the hypo- 

 thetical ancestral trace. The rest of xylem of the trace is regarded 

 as centrifugal. Isabel M. P. Browne (London). 



Gwynne-Vaughan, D. T., On some climbing Davallias and 

 the petiole oi Lygodium. (Ann. Bot. XXX. N» CXX. Oct. 1916.) 



It has been explained by the present author and Mr. Kids ton 

 that the Osmundaceous trace can be derived from an hypothetical 

 ancestral form, the solid xylem of which was more or less rounded 

 or elliptical in transverse section. M. P. Bertrand has shown that 

 the Botryopteridean and Anachoropteridean traces can be derived 

 from a similar hypothetical form. In seems probable that the traces 

 of the great majority of the living forms may be regarded as var- 

 iants of the C shaped Osmundaceous trace. In the Schisaeaceae 

 Aneimia has a C shaped trace; but according to most authors the 

 traces of Lygodimn and Schisaea are of an absolutely different type 

 Mm. C. E. Bertrand and Cornaille, however, have offered a 

 remarkable explanation of how the peculiar trace of Lygodium may 

 be derived from one of the complex variants of the C-shaped type, 

 of trace. According to them the inverse folds of the more compli- 

 cated Polypodiaceous and Cyathaceous traces has led by increase 

 of metaxylem to the union, in the median plane, of the two sides 

 of the fold, thus producing the solid hexagonal trace of Lygodium^ 



