. Biology; the story of living things. THE DEVELOPMENT OF SEXUALITY IN PLANTS 169 cellular forms to some of the great brown seaweeds, or kelps of the California coast which may be several hundred feet in length. Ascending the scale of increasing complexity in structure, we find the appearance first of sex cells and later of sex organs evolved to form and protect these sex cells. By selecting other representatives from the higher plant groups, such as mosses, ferns, and flowering plants, we can follow this evolu- tion of sex through the entire plant kingdom. The pages that follow will at least
. Biology; the story of living things. THE DEVELOPMENT OF SEXUALITY IN PLANTS 169 cellular forms to some of the great brown seaweeds, or kelps of the California coast which may be several hundred feet in length. Ascending the scale of increasing complexity in structure, we find the appearance first of sex cells and later of sex organs evolved to form and protect these sex cells. By selecting other representatives from the higher plant groups, such as mosses, ferns, and flowering plants, we can follow this evolu- tion of sex through the entire plant kingdom. The pages that follow will at least give us a start on the answer to the question : How and where does sex originate in plants and what is its meaning ?. The Beginnings of Sex in the Algae Pleurococcus, or Protococcus as it is sometimes called, is one of the simplest of all living plants, familiar to most of us as the green "moss" usually seen on the north side of trees. Indians used it to find their direction through the forest, as persons lost in the woods do today. Its habitat suggests that the life of the plant has direct relation to moisture, temperature, and light. It would be injured by the direct rays of the sun, because some rays such as those of ultraviolet light are injurious to unprotected protoplasm. The cell of Pleurococcus is very simple as seen under a microscope. It is found single, in twos, threes, fours, or flat colonies of several cells hanging together. Examination of a single cell discloses the presence of a thin wall sur- rounding a mass of green protoplasm, the protoplast, which almost completely fills the cell. If a drop of iodine solution is placed under the coverslip, the detailed structure of the cell becomes more evident. The nucleus is completely surrounded by one large, spherical chloro- plast. The cell is a complete entity, in spite of the fact that it is often attached to other cells. Physiologically it is able to carry on all the functions of a living green plant, makin
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