Sex and the Single Cryptogam j 469469 469
[l] ively imagination, most likely accompanied by a faulty microscope and incorrect
preparation of samples, have led Sumiński to the curious belief that the mobile spiral
threads enter the fern’s germinal organs.^17To Schleiden, the take- home message from the “cryptogams” was not that they possessed
sexual organs, which he denied, but that they reproduced asexually via spores. According to
Schleiden, asexual spores, not seeds, were the primary units of propagation— not only in the
cryptogams, but in seed plants as well!Figure 17.3 Stages of asexual reproduction in the life cycle of a fiddlehead fern. A. Mature fern
fronds (leaves) grow out from underground stems called rhizomes. B. Sporangia are grouped in
clusters called sori (si ng u la r, sorus) on the underside of the mature fern frond. C. At maturity,
the sporangia break open and disperse their spores to the ground.^30 D. The spores germinate on
the ground, forming a short, multicellular filament called a protonema. E. The cells at the tip of
the protonema begin dividing laterally to form a small, flattened, heart- shaped structure called
a prothallus. F. The prothallus expands and forms root- like rhizoids and sexual structures (not
labeled) on the underside of the prothallus.