280 MR. A. S. HORNE— A CONTRIBUTION TO 



as a separate organ, forms only a small portion of the ovule, as in Davidia. Its 

 l3oundarv, I, is indicated in Text-fig. 13, B. The embryo-sac, as sho-^ni in PI. 29. fig. 74, 



immediately subjacent to the epidermis of 



Only one epidermal cell is 



shown in the figure, and no trace of a cap formed from sterile megaspores nor traces of 

 parietal tissue are evident. The embryo-sac itself exhibits no noteworthy departure 

 from the normal. 



Vascular Structure, 



The vascular tissue of the pedicel in the female flower separates into a peripheral 

 and an axial (ax) series of bundles (Text-fig. 9, A). There are ten outer and five 

 inner bundles in pentamerous flowers, but the number in each series varies with the 

 carpels; in the case of the exceptional flower noted above [Helwingia^ text, p. 278), the 

 bundle corresponding to the missing sepal was absent. The bundles of the outer series 



pposite the loculi (B, d) take an upward 



branching, into the style (F) 



and stylar lobes — one into each, corresponding to dorsal carpellary bundles; those 

 alternating with the loculi (B, se) extend upward also without branching and enter the 

 sepals. 



The bundles of the axial series (B, ax) are opposite the loculi. Each one extends 

 axially as far as the corresponding placenta, forms three branches of which the median 

 becomes the ovular bundle, whilst the lateral branches (C, E, I) pass outwards, and 

 ultimately join the corresponding dorsal bundle (E). 



Two interpretations of the vascular structure may be presented, and until more 

 extended investigations have been made claim equal attention. The first is suggested 

 by a comparison with Aralia and Nyssa. As in Aralia^ the traces are free, and when 

 the number of carpels and perianth segments deviates from the normal the traces vary 

 correspondingly. A transition from hermaphrodite to female flowers occurs in Nyssa^ 

 wlien both the stamens and stemonal traces disappear; so Helwingia^ by analogy with 

 Nyssay may have lost both stamens and petals, together with their traces, when epi- 

 gynous. The second and perhaps a more tempting solution is to suppose, by analogy 

 with Garrya, that the flower was already apetalous and unisexual in its hypogynous 

 state, in which case petal and stemonal traces have never existed in the ovary-wall. 



Morphology of the JPerianth. 



Lindley * compares the perianth with the supposed calyx of Garrya. Bentham and 

 Hooker t, on the contrary, hold that it is homologous with the corolla of Meryta,Q>g&n\M& 

 of the Araliacea3. Both genera are placed side by side in the Araliaceaa for the following 



reasons :— (1) "^^^ perianth leaves alternate with the stamens in both genera, and the 

 aestivation is valvate ; (2) in Meryta both calyx and corolla are present in the male 

 flower, although the calyx is absent in the female flower. Bentham and Hooker deduce 

 that the calyx, already obsolete in the female flower of Meryta^ has entirely disappeared 



• J. Lindley, Veg. King. 2ad ed. 295 (1847). 



t G. Bentham et J. D. Hooker, Gen. PI. i. (1867) 940. 



