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TEXTBOOK OF BOTANY 



ImM 



Fig. 315. Resurrection plant (Selaginella) of Texas and New Mexico. During 

 the rainy season the plant spreads out and grows as a rosette. When drought 

 comes, it dries out and curls up into a ball, as indicated at the right. Courtesy 

 World Book Co. 



Fossil imprints of the ancestors of the lycopods are very abundant 

 in Carboniferous rocks. Fossil remains indicate that during this period 

 hundreds of species of club mosses were dichotomously branched trees 

 up to several feet in diameter and a hundred or more feet in height. 

 The leaves were somewhat scale-like, arranged in spirals or in whorls, 

 and often a half-foot long. The number of species of present-day lyco- 

 pods, all of which are small plants, is estimated at about 600. 



The sporophyte. Both Lycopodiiim and Selaginella consist of a much- 

 branched, creeping or erect stem, practically covered by small scale-like 

 leaves attached by a broad base. The adventitious roots are filiform and 

 develop from the under side of the stem in contact with the soil or in 

 moist air. Both the stems and leaves have a fundamental structure 

 similar to that of seed plants. The more primitive species have rather 

 large sporangia in the axils of leaves; in the more specialized types the 

 sporophylls are small, often non-green, and arranged in compact cones 

 at the ends of upright branches (Fig. 316). 



In Lycopodium four spores are produced from each mother cell in 

 the sporangium, and all the spores are alike morphologically and physio- 

 logically. Consequently Lycopodium is said to be homosporous. In 

 Selaginella the spores are of two kinds formed in different sporangia. 

 The small spores ( microspores ) develop by the hundreds in small spor- 

 angia ( microsporangia ) , and four large spores (megaspores) develop 

 in each large sporangium ( megasporangium ) . Selaginella is thus het- 

 erosporous. 



