Harper . — Cell-Division in Sporangia and A sci. 501 
late in the afternoon, and continues gradually to enlarge 
during the night (Fig. 10). It is lined by a protoplasmic 
layer no thicker nor more numerously supplied with nuclei 
than the remainder of the sporangium. The cell-wall of the 
narrow neck between this vesicle and the sporangium is very 
thin, indicating the line of fracture when the vesicle finally 
bursts. The central vacuole of the vesicle contains only 
cell-sap, the protoplasmic primordial utricle forming only a 
lining layer just inside the wall. The throwing off of the 
entire sporangia during the morning hours by the swelling 
of the collar and bursting of the vesicle beneath, and the 
wonderful heliotropic reactions they show in the direction 
of the discharge, have been fully described by Brefeld. During 
ripening the sporangial wall has become very much thickened 
and brittle over the top of the sporangium. It thins out 
rapidly, however, and is light- coloured beneath the collar, 
and offers less resistance to the swelling of the latter at the 
time of the explosion. 
The germination of the spores in a decoction of horse-dung 
can be readily studied in all its phases by fixing in Flemming’s 
solution, fastening them to the slide with albumen-fixative, 
and staining with Flemming’s triple stain or Mayer’s c Car- 
malaun.’ The spores swell tremendously before pushing out 
a germ-tube, and the two nuclei divide to form eight or more. 
‘ Carmalaun ’ gives the best results for staining the swelling 
stages, but Flemming’s stain serves better after the germ-tube 
is formed. Figs. 25, 26, and 27 show these germinating 
stages. The nuclei may be readily demonstrated at these 
stages, but the plasma is too dense and the wall too impene- 
trable to allow a full study of their division. The develop- 
ment of the living spores can be well watched in their earlier 
stages under an immersion lens, and Figs. 28 to 29 show the 
appearance of spores of an undetermined species of Pilobolus 
during germination in water. As soon as the spores swell 
the nuclei can be made out without staining. They undergo 
considerable amoeboid changes of form, and seem even to 
change position in the spore by this means. In this case 
