146 Johnson . — On A rceuthobium Oxycedri . 
gonum 5 [and like it formed of the modified apex of the floral 
axis l ]. 
Treub cannot think that the ovarian papilla in Loranthus 
sphaerocarpus is an ovule ; the hypothesis which he suggests 
is this 2 : ‘La region axile du mamelon, constitue un placenta, 
et les trois ou quatre segments lateraux libres, qui se pro- 
duisent, sont des ovules rudimentaires. La plurality des 
cellules-meres de sacs embryonnaires, dans chaque segment 
empeche d’assigner le rang d’ovules aux sacs embryonnaires 
memes.’ In support of this hypothesis Treub found the 
ovules (usually four) in Loranthus sphcerocarpus represented 
by distinct lobes near the apex of the placenta. In each 
lobe there was a large number of embryo-sac mother-cells 
side by side, of which only one gave a fertilisable embryo-sac. 
There are no lobes on the papilla in A. Oxycedri. The two 
embryo-sacs are separated by uniform tissue, each one is 
apparently derived from a unicellular hypodermal arche- 
sporium, and so in this respect there could be no objection to 
regard each embryo-sac as an ovule. It would not be a long 
step from Loranthus sphaerocarpus to A. Oxycedri , thus passing 
to a placenta bearing two completely imbedded ovules reduced 
in each to a single archesporium cell. 
Several objections may be urged to the view that the 
papilla in A. Oxycedri is an erect orthotropous ovule con- 
taining two fully developed embryo-sacs. There is no 
example in the Phanerogams of an ovule containing two 
such embryo-sacs. It would be a forced comparision to 
regard the condition in A. Oxycedri as capable of expla- 
nation by reference to the macrosporangium of Isoetes. The 
nearest approach to this structure of an ovule is that de- 
scribed by Strasburger for the ovule of Rosa livida 3 . In 
this plant there is a multicellular archesporium forming 
(generally) four embryo-sac mother-cells lying side by side. 
Of these only one, after they have all passed through one or 
1 Strasburger, Die Angiospermen u. d. Gymnospermen, p. 3. 
2 Treub, in Annales du Jard. Buitenzorg, ii. p. 64. 
3 Strasburger, op. cit, p. 14. 
