MR. G. BEXTItAM ON MTItTACE^. 110 



a single, ampliitropous, broad, almost orbicular ovulo, peltatelj 

 attached to the centre of the disk of an orbicular peltate placenta. 

 This curious-looking arrangement strikes at first as a remarkable 

 anomaly; but a careful examination shows in most species a pair 

 of more or less abortive ovules near the upper margin of the 

 placenta, concealed under the perfect peltate ovule, or sometimes 

 shortly prominent in B, deciissata and B. sqtiarrosa. In the ad- 

 joining genus Begelia^ these two upper ovules become perfect, as 

 well as a fourth, collateral with the perfect one of Beaufortia^ 

 bringing the arrangement to the ordinary two rows of amphitro- 

 pous ovuleSj all in this case peltate. 



In the unilocular Chamrclaucleae the ovules are always more or 

 less amphitropous, and in pairs or in two rows. In the subtribe 

 Euchamtelauciea? the eccentrical placenta, either short, basal, and 

 free, or adnate to the wall of the cavity on one side, but not 

 extending to the summit, shows pretty clearly that we have liere 

 a gyna^cium reduced to a single carpel; and the placentatlou is 

 thus normal. But in Cahjtlirix and Lhotzkya (forming the sub- 

 tribe Calythriceso) the two ovules, although still amphitropous, 

 are quite straight and collaterally affixed to a filiform placenta, 

 attached to the base and summit of the cavity, but usually free 

 from its walls, although sometimes excentrical ; and the (question 

 arises, does this placenta represent the single placenta of the 

 monocarpellary Euchama?laucie£e, or is it the reduced dissepiment 

 of a bicarpellary ovarium with uniovulate cells, like that of somo 

 species of Scholtzia ? And the problem is not satisfactorily solved 

 by the examination of the three connecting genera, Tfomalocalj/Xj 

 Thri/^fomene^QinA Micromyrtus^ provisionally grouped in the third 

 subtribe Thryptomeneae. All three have the habit of Bwckea ; 

 llomalocalyx \i^^ the stamens of Calythricea) with the placenta- 

 tlou of Euchamaelauciese ; Thryptomene has tlie stamens of BcerJcea 

 with the placentatlou of Eachamcelauciea? ; 2Iicromyrtiis has also 

 the stamens of BcBcJcea^ but with a placentation directly con- 

 necting Calythriceae with Schollzia, 



Generally speaking, these modifications of the ovules and their 

 placentation afford the best generic characters, the most in ac- 

 cordance with minor characters and general habit. I have ana- 

 lyzed the ovaries of nearly GOO Australian species, aiul generally 

 from many different specimens of each, and have found no other 

 organs so constant, provided too much weight be not attached to 

 the precise form of the placenta, which is \GYy variable in BdcJcea 

 and some other large genera. This importance of placentation 



