56 



DUDLEY MEMORIAL VOLUME 



The seta at this stage has about the same length as the capsule, and in 

 longitudinal section (Fig. 12, H) shows the cells to be arranged in pretty 

 regular rows. Probably the great elongation of the seta at the time the 

 spores are shed is due to simple elongation of the cells without any cell divi- 

 sions, as has been shown to be the case in other liverworts. The large heart- 

 shaped foot (f) is composed of somewhat irregular cells showing no defi- 

 nite arrangement. 



Fig. 11. Spore division. A, spore mother cell, showing the quadripolar spindle, 

 x 750. B, three spore mother cells of about the same age, showing the different 

 arrangement of the lobes of the cell, x about 350. C, young elater. D, spore mother 

 cell, showing the chromosomes. E, a somewhat earlier stage. F-I, successive stages 

 of mitosis with quadripolar spindle. In G and H the chromosomes only are shown. 

 /, mother cell with the lobes in pairs; there are two nuclear spindles at right 

 angles to each other. K, mother cell, showing a bi-polar spindle at the first mitosis. 

 L, first mitosis, showing two nuclei separated by a distinct cell-plate, x about 400. 

 M, mother cell just before the final separation of the spores, x 400. 



