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PROTEROGYNOUS and PROTOGYNOUS

(from proteros, sooner, and gyne, a female).

Terms used, by Delpino and by Hildebrand respectively, to denote a hermaphrodite flower in which the stigma is ready to receive pollen before that in the same flower is ripe. In Proterogynous flowers, the stigma is pollinated from an older flower, and may be withered, or may have fallen off, before the anthers in its own flower have burst to shed the pollen. Proterogyny is not frequent. The common Pellitory (Parietaria officinalis) affords an example.

PROTHALLUS, or PROTHALLIUM (from the Greek words pro, instead of, and thallos, a branch; in reference to the structure thus named taking the place of a stem). The body which is developed from a spore of a Fern, Horsetail, Club-moss, or Pillwort. It varies much, in these four groups, in its degree of development, and in its form; but, in all cases, it is entirely cellular throughout its existence, and on it are formed the organs for sexual reproduction. In Ferns, the male and the female organs are present in the same Prothallus; in most plants of the other groups, the Prothallus bears only male or only female organs. There is a distinct alternation of generations in plants that produce a Prothallus, i.e., in the higher Cryptogams. The spore produces the Prothallus (see. Fig. 290), on which are formed the sexual organs, the male being the antheridia, with antherozoa, and the female being the archegonia, in each of which lies the oosphere, which, fertilised by antherozoa, becomes the oospore. This develops into the Fern-plant bearing the well-known fronds, on the back of which are visible the groups (sori) of minute, brown spore-cases (sporangia), in which lie numerous spores, like the one with which the cycle began. The spores are formed by vegetative growth, not by sexual reproduction. It will thus be seen that the Prothallus and the leafy Fern-plant are two generations in the course of a single cycle. The