192 Plant Biology 



9. In ferns and their allies the multicellular sporangia (spore cases) 

 are usually borne on leaves so that such sporophylls are an important 

 characteristic. 



10. In certain species the sporophylls bear sporangia in which the 

 spores are all alike (homosporous) ; in others there are two kinds of 

 sporophylls, two kinds of sporangia, and two kinds of spores (hetero- 

 s porous). 



11. Sporangia may (1) be borne in clusters (sori), as in ferns, (2) 

 occur in groups of 5 to 10 upon shield-shaped sporangiophores to form 

 conelike strohili, as in horsetails, or (3) occur singly on the upper sur- 

 face of the sporophylls to form a clublike strobilus, as in club "mosses." 



12. Spores germinate to form different types of young gametophytes : 

 ( 1 ) colorless, rather bulky prothalli with male antheridia and female 

 archegonia in club "mosses," (2) thin, green, irregular gametophytes, 

 with antheridia and archegonia in horsetails, (3) small, thin, green, 

 heart-shaped prothalli with antheridia and archegonia in ferns. 



CLUB "MOSSES" 



1. Lycopodium (laik o -po' di um) (Gr. lykos, wolf; pous, foot) . — The 

 club "mosses" belong to the subkingdom Embryo phyta because they pro- 

 duce multicellular embryos, to the phylum Tracheo phyta because they 

 possess true vascular tissues, and to the subphylum Lycopsida (laik -op' 

 si da) (Gr. lykos, wolf; opsis, appearance) . 



Plants belonging to the genus Lycopodium (Fig. 47) are small and are 

 commonly called club "mosses'' because of the mosslike leaves and the 

 club-shaped cones (strobili) borne on stalks. They are also referred to 

 as "ground pines" because of their /)ro5/;'<2^^^ creeping habits and their 

 resemblance to evergreen, miniature pine trees. The main stem (rhi- 

 zome) is prostrate on the ground and is branched. It possesses roots 

 and sends up numerous upright stems, usually about eight inches tall. 

 The upright stems bear small, green leaves, usually spirally arranged. 

 Lycopodium possesses a simple vascular system consisting of alternate 

 strands of phloem (sieve tubes and companion cells) and xylem (tra- 

 cheids). Stomata occur on the leaves and stems for the exchange of 

 gases. 



Sporangia-bearing leaves are known as sporophylls. In some species 

 the single sporangia are borne on leaves which may be located on any 

 part of the stem. In other species the sporophylls are concentrated at 

 the tips of the branches to form conelike strobili. The spores are all 



