466 i Flora Unveiled
But this interpretation also had its problems. As a champion of the sexual theory, Linnaeus
believed that seeds in flowering plants were produced by flowers. If the tiny particles of moss
powder were indeed seeds, then they should have been formed by a process resembling polli-
nation. But, try as he might, Linnaeus could find neither stamens nor pistils anywhere on the
leafy structures of mosses. Convinced that sex was universal and that male and female sexual
organs must be present, he contented himself with placing mosses in the Cryptogamia group.
Meanwhile, French botanists correctly identified the powder produced by mosses, ferns, and
other cryptogams as asexual spores. In their natural systems of classification, French bota-
nists regarded the cryptogams generally as asexual. This was a direct challenge to Linnaeus’s
idea that sex was universal in the plant kingdom. Thus, by the early nineteenth century, the
debate over plant sex had begun to shift from angiosperms to cryptogams.
The main barrier to discovering the sexual organs of the cryptogams was that they were
invisible to the naked eye, and botanists were hampered by the poor quality of their micro-
scopes. As microscopes gained in resolving power, botanists began to train their improved
F igu r e 17. 1 Stages of asexual reproduction via spores in the life cycle of a typical moss. A. In the
spring, a spore- containing capsule (sporangium) attached to an elongated stalk grows out of the tips
of the leafy structures of mosses. B. At maturity, the outer covering of the capsule, the calyptra, is
shed, and a circular lid (the operculum) pops open. C. The released spores fall to the ground. D. The
spore germinates on the soil, forming a multicellular filament, the protonema. E. Certain cells of
the protonema develop tiny buds. F. The buds grow up into new leafy structures. In addition, root-
like rhizoids grow below the buds, anchoring the moss plant to the ground. See the insert for color
figures of the life cycles.