Ferns and Their Allies 193 



alike (homosporous) and are wind disseminated. A spore germinates to 

 form a colorless, rather lumpy prothallus (young gametophyte) which is 

 usually in the soil. In some cases a small part of the inconspicuous 

 gametophyte is above the ground and is green. 



Male antheridia and female archegonia similar to those of the Bryo- 

 phytes are embedded on the upper surface of the gametophyte. Rhi- 

 zoids anchor the gametophyte. The antheridia produce hiflagellated 

 sperms (like those of true mosses) that swim to the egg which is fer- 

 tilized to form a zygote. 



By cell division the zygote forms two cells, one of which forms a sus- 

 pensor which pushes the embryo into the food tissues of the gametophyte. 

 The other cell forms the multicellular embryo which develops into a 

 young, leafy sporophyte. The latter remains as a temporary parasite 

 on the gametophyte. The embryo forms a special organ called the foot 

 which acts as an absorbing organ. A root forms and the gametophyte 

 tissues eventually decay, thus leaving the herbaceous sporophyte inde- 

 pendent. 



The various species of Lycopodium are common plants of forests and 

 mountains. They are widely used in the preparation of decorations, 

 wreaths, and other articles where the evergreen stems can be used. 



2. Selaginella (sel i ji -ncF a) (L. selago, shrubby plant). — The deli- 

 cate, perennial, smaller club "mosses" belong to the genus Selaginella 

 (Fig. 48) and are widely distributed but are most abundant in the 

 tropics. One species of Selaginella, known as the "resurrection plant," 

 can withstand dry conditions in southwestern United States by rolling up 

 into a ball. Other specimens are grown as ornamental plants in green- 

 houses. 



Most species of Selaginella are usually creepers, although a few are 

 erect. The stems are branched, wdth tiny, green, triangular, stomata- 

 bearing leaves, usually in four rows. Roots anchor the plant and absorb 

 materials. The vascular system is rather simple and varies with the 

 species. At the base of each leaf is a membranous ligule (lig' ul) (L. 

 ligula, little tongue) of unknown function but of value in differentiating 

 Selaginella from Lycopodium which lacks this structure. 



Cones at the tips of the branches are composed of spore-producing 

 sporophylls. In a cone the upper surface of each microspore phyll has 

 in its axil (upper angle) a small micros porangium which produces many 

 small microspores. The larger megasporophylls produce four large mega- 

 spores in each me gas porangium located in the axil. Frequently, the 

 microsporophylls are located toward the tip of the cone, while the mega- 



