THE STUDY OF THE EVOLUTIOI^ OF THE FLOWEE. 269 



(c) AUCUBA. 



MorpJiology of the Flower and Ovule. 



Tlie plants are unisexual, and tlie bracteate flowers are borne in compound cymose 

 racemes with branches arranged decussately. The female inflorescence bears a number 

 of minute rudimentary, as well as perfect flowers. The male flower consists of 

 alt.ernatiniT tetramerous whorls of sepals, petals, and stamens, the female of a 



unilocular ovary with alternating epigynous tetramerous wliorls of sepals and petals. 

 A few hermaphrodite flowers bearing two or three stamens were found on the female 



plants of A 

 oblique 



giWV, XX.J3 



at Kew in 1910. The ovary terminates in a style with 

 points towards the placental side of the ovary. Payer and 



Eichler state that the placenta is directed away from the bract ; Baillon, that it may be 

 directed awav from the bract, towards it, or laterally ; the writer finds that it may 

 occupy any one of the four antepetalous or altcrnipctalous positions. Hence the 

 orientation of the ovary relative to the perianth is variable. The development of the 

 flower has been accurately described by Payer— its primordium resembles an incomplete 

 circular ridge (this becomes circular with an oblique opening) ; as growth proceeds, the 

 mamelon becomes ovoid enclosing a cavity— the loculus,— and the narrow orifice forms 

 eventually the slit-shaped stylar canal. The placenta, which is terminal and bilobed in 

 transverse sections of mature ovaries, arises as a well-defined bulge from the ovary-wall. 

 The sino-le descendinj? ovule develops at the end of this protuberance. The ovaries are 



_.v^ ^^^^-^^^^^^^ 



very rarely biovulate. One biovulate ovary was found in A. japonlca—ihG additional 

 ovule developed from a placenta on the opposite wall of the loculus, but the ovary 

 remained unilocular ; the stigma was unequally bilobed. Two out of twenty ovaries 

 were biovulate in A . Umalaica ; the stigmas were irregularly lobed— perhaps an abnormal 

 feature, since a capitate stigma is figured in Hooker's * illustrations of this species. 



The earliest stages in the development of the ovule, prior to the differentiation of the 

 nucellus, are shown, in vertical section, in Text-fig. 18, P, G. The pivot-cells at the 

 point where the mamelon bends away from the ovary-wall are indicated at p. In 

 G the portion of the mamelon below the pivot-cells shown in P has elongated con- 

 siderably, owing to cell-division, and three regions of special merismatic activity are to 

 be observed. The lowermost of these is localised at nn hit, which is the primordium of 

 the lower rim of the integument ; the next is confined to the primordium of the 

 nucellus, nu ; the third and uppermost, up int, extends from the upper edge of the 

 nucellus to the pivot-cells on the adplacental side of the ovule. Here the cells are 

 providing for horizontal extension. The next stage (D) shows the ovule after con- 

 siderable growth has taken place ; the chalazal region is now clearly defined and 

 the nucellus has turned through an angle of 45^ This has been accomplished by 

 the lon-itudinal elon-ation of the abplacental [ah) end of the ovule durmg 



differentiation, whilst the adplacental {ad) side has undergone less longitudinal, but 



J. D. Hooker, Hlustr. Himal. Plants, 12. 



