STIGMA AMJ I'AIUKTAI; I'J^ACKN'JVE IN PLANTS. 551)
being obviously so in ajiiiiy cases ; iind in one genus at least, Ihsniannia, it extends nearly the whole length of the ova- rium, so as to be coiiiinensurate with and placed cxactlv o])])osite to the internal polyspernions ])lacenta.
That the stigma is always double aj)i)cars probable t'loni those cases in which it is cither completely developed, as in the greater part of Gramincce where the ovarium is sim[)le ; in the compound ovarium in Urnia ; and from those in which the development, though less complete, is still sutticiently obvious, as in many I'Jffp/iorbiacece and in several Tridece. This degree of development, however, is comjjaratively rare, conliueiice between the two stio-mata of each cai'pel beiufj the more usual stiucture ; and in the compound pistillum a greater degree of confluence often takes j)lace in the stigmata than in the placentic; — a fact, which in all such cases is obviously connected with adaptation of surface to the more complete performance of function.
Another difference frequently occurs between the mode of confluence of placentae and stigmata, namely, that in the compound but unilocular ovarium, while the placentte of the adjoining carpels are united, the stigmata of each car[)el are generally confluent. But this rule admits of exceptions, as in Parjia-stiia, in many Cruci/erce, and in Papaccrcuece ; in all these cases the stigmata as well as placentae of the adjoin- ing carpels are confluent, a structure satisfactorily proved in i'ruL'iferce by several cases of monstrosity, in which the stamina are transformed into pistilla; and in Papavcracece by a series of modifications of structure as well as by a like transformation of stamina.
A similar confluence of stigmata in the compound mul- tilocular pericarpium is of much rarer occurrence; it is foiuid, however, in the majority of Iridece, in which the three stigmata alternate with the cells, and consequently with the placentae of the trilocular ovarium. Tliat this is the correct view of the composition of the stigmata in Tridece is at least probable from their occasional deep division, and more par- tictdarly still from the bifid petal-like styles or stigmata which are op})osite to the cells of the ovarium in other genera of the same familv, as in Iris and Monca. In both these
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