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A TEXTBOOK OF BOTANY 



[Ch. XI 



the under side (morphologically the upper) of the female 

 receptacles. The fertilization requires water, e.g. heavy 

 rain, and when conditions are favorable, the archegonia 

 eject diffusable substances attractive to the sperm cells, 

 which enter the neck, — the first to reach the egg cell effect- 

 ing fertilization. The fertilized egg cell grows at once to a 

 somewhat elaborate sporogonium, comprising a wall, a 

 chamber containing many spores intermingled with hy- 

 groscopic elaters, and ultimately an elongated stalk, at 

 the base of which persist the membranous remnants of the 

 archegonium. This sporogonium represents clearly the 

 sporophyte, just as the thallus is the gameto- 

 phyte. When ripe, the spore capsule bursts open, 

 and the hygroscopic movements of the elaters 

 force out the spores, which are disseminated by 

 the wind, and on germination produce new thalli. 

 In the Marchantia occurs also a well-developed 

 vegetative reproduction by gemmae, as earlier 

 described (Fig. 211). The mode of growth of 

 the perennial thallus incidentally effects the 

 same end, for the death of the older parts results 

 in separation of the lobes. 



Order 3. J ungermanniales : the Leafy Liver- 

 worts, or Scale Mosses. These are the most 

 abundant Liverworts, numbering some 3000 

 species. They are mostly tropical, and 

 grow not only on the ground, 

 but also epiphytically on the 

 trunks and even the leaves of 

 trees ; and very pretty forms 

 occur in our own woods, mostly 

 among the true Mosses on old 

 fallen logs. While some are 

 thallose, as in the preceding order, they are usually, and char- 

 acteristically, differentiated into slender, creeping stems bear- 



Fig. 341. — A leafy Liverwort, 

 Gottschea appendiculata, with opened 

 sporogonium ; somewhat reduced. 

 (From Le Maout and Decaisne.) 



