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, making food, and digesting 

 it as well as absorbing food and water. It grows to a certain size 

 and then reproduces by simple fission, part of the mother cell going 

 into one daughter cell and part into the other. Theoretically the 



Reproduction in Pleu- 

 rococcus. Each cell is 

 considered as an indi- 

 vidual, although colonies 

 (seen above) may be 

 formed. The protoplasm 

 of the cell body is not 

 shown, the single chloro- 

 plast being surrounded 

 by protoplasm in active 

 cells. 



