34 



GENUS PALLAVICINIA 



convex disk, which in section (Fig. 18, B) appears as a broad band of 

 narrow cells in vertical rows. Some of these cease to divide, and later 

 become much elongated, giving rise to the elaters ; while the others, 

 dividing by transverse walls into rows of isodiametric cells, become the 

 mother cells of the spores. In P. radiculosa the sporogenous region, even 

 at first, is more extensive than in P. Zollingeri. 



Fig. 20. Pallavicima Zollingeri. 



in, involucre ; per, perianth. 



A. Young sporophyte still enclosed in the calyptra 



B. Open capsule, showing the four coherent valves. 



C. I, section ; II, surface view of ripe spores. 



D. Elater. 



By the time that the perianth is fully developed the sporophyte, 

 closely invested by the calyptra, reaches about half-way to the top, and 

 the separation of the sporogenous tissue into the spore mother-cells and 

 elaters is plainly evident (Fig. 19, A, B). By the time that the sporo- 

 phyte emerges from the perianth the spores have passed the final stage 

 of division and are nearly mature. The material of P. Zollingeri did not 

 furnish preparations showing the details of mitosis in the final stages 



