Metapliyta Polytrichiim. 1 09 



for a time, and then drops off. It will now be necessary to 

 study this product of sexual union, an organism, it is to be 

 noted, quite different from the thallus which produced the 

 sexual cells and which now bears the embryonic new gene- 

 ration as a parasite on itself. 



As already stated, the new generation consists of a stalk, 

 or seta, surmounted by a capsule, or theca. The seta is fixed 

 firmly in the basal portion of the venter, and consists of a 

 core of slightly elongated cells covered by a thickened 

 epidermis. The seta swells slightly below the theca forming 

 the apophysis. The seta is continued up through the theca 

 as the columella. Surrounding the columella is an annular 

 spare traversed by thread-like ceils, which stretch from the 

 columella to the outer wall of the theca. The wall of the 

 theca is several layers of cells deep, and has its epidermal 

 layer strongly thickened. Closely surrounding the colum- 

 ella, but separated from the annular air-space, by two or 

 more layers of cells containing chlorophyll, forming the 

 spore-sac or sporangium, lies a layer of cells which are 

 highly protoplasmic and are capable of active division 

 This forms what is known as the archesporium (fig. 40). 

 These cells do not become spores directly, but give rise to 

 what are known as mother spore-cells lying in the interior 

 of the now much enlarged sporangium. The walls of the 

 mother spore-cells deliquesce, or become watery, forming 

 a fluid medium in which float the rapidly developing spores, 

 formed by subdivision into four of each of the mother 

 spore-cells. The upper part of the columella is much 

 enlarged, and forms a disc covering the sporangium and 

 its contained spores. The margin of the disc-like head of 

 the columella becomes continuous with the outer wall of 

 the theca, which is itself in this region greatly modified. 

 The terminal pointed portion of the theca separates as a 

 lid or operculum. At the point of junction between the 

 operculum and the theca, there is developed a series of 

 multicellular hairs, the>e^^aJla;O^which are thickened and 



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