(801

(801 (656

Ch. XII

Gen Con

native homes, and with plants a little more or less manure, water, heat &c. We see how sensitive the sexual elements must be of those plants, which are completely sterile with their own pollen, but are fertile with that of every any other individual of the same species. Such plants become either more or less self-sterile, have their self-sterility if subjected to new changed conditions, although the change may not be great.

The ovules of a heterostyled trimorphic plant are affected very differently by pollen from the three sets or continues four sets of stamens in the flowers of belonging to the same species. With ordinary plants the pollen of another variety of or merely of another individual of the same of course is variety is often strongly prepotent over that pollen from the same flower or plant when both are placed at the same time on the same stigma. In those great families of plants containing several many thousand allied species, the stigma and ovules of each distinguishes with unerring certainty its own pollen from that of all every other species.) Why there should we feel any surprise at this sexual element of three forms which we call