322 HOFMEISTER, ON 



divide by septa parallel to the outer surface (PI. XLIII, 

 tigs. 7 9). The four cells which project beyond the apex 

 of the larger cell expand above in a papillate manner 

 (PI. XLIII, fig. 5), after which each of them divides by a 

 transverse septum (PL XLIII, fig. 4). All the cells of the 

 prothallium, with the exception of these papillate cells and 

 the large central one, form chlorophyll granules in their 

 interior. 



The increase in the circumference of the pro-embryo causes 

 a bending back of the surrounding pointed shreds of the inner 

 layer of the outer spore-membrane. The pro-embryo be- 

 comes visible in the form of an emerald-green wart at the 

 apex of the germinating spore. The four papillate cells at 

 the apex of the pro-embryo, and their four basal cells, now 

 part asimder at the commissure, and thus an open canal, 

 leading to the large central cell of the pro-embryo, is pro- 

 duced (PL XLIII, figs. 8, 9). Some of the papillate cells 

 sometimes divide now by a second transverse septum 

 (PL XLIII, fig. 9). A daughter-cell is in the mean time 

 formed within the large central cell, the contents of which 

 latter cell are finely granular and mucilaginous. This 

 daughter-cell soon after its formation almost entirely fills 

 the mother-cell (PL XLIII, figs. 8, 9). The central cell of 

 the prothallium, and the four projecting cells, constitute the 

 archegoniiun. The prothallium of Pilularia never produces 

 more than one archegoniiun. 



The development and structure of the prothallium of 

 P. minuta entirely resemble those of P. globulifera as far 

 as my observations extend, with the single exception that 

 the base of the prothallium in the former is somewhat more 

 strongly constricted than in the latter, so that the prothal- 

 lium appears more spherical. 



The small spores swell slightly after becoming free. The 

 outer spore-membrane splits at the apex, forming three 

 fissures, the direction of which corresponds to the edges of 

 contact of the spore with the three sister-spores produced 

 in the same mother-cell. The inner spore-membrane 

 bursts, and some small spherical cells escape from the 

 inner cavity of the spore ; these cells contain small starch - 

 grains and a lenticular vesicle attached to the wall (PL 



