388 HOEMEISTER, ON 



guished in any respect from the others,* becomes slightly 

 increased in diameter, its primary nucleus becomes dis- 

 solved, and four new nuclei are formed. This cell then 

 divides into four tetrahedral daughter-cells, the special- 

 mother-cells of the spores, by six septa cutting one another 

 at angles of 120 (PL LV, fig. 7). Almost immediately 

 afterwards there is formed in each of the special-mother- 

 cells a cell almost filling the latter, and having at first very 

 delicate walls. This cell is the spore. The four spores 

 immediately begin to become individualised by the gradual 

 dissolution of the wall of the special-mother-cells (PL LV, 

 figs. 8, 9, 10), and they assume a spherical form. The 

 loci of the commissures of the special-mother-cells are 

 indicated by very slightly prominent ridges (PL LV, figs. 

 II 6 , 12*). The product of the dissolution of the special- 

 mother-cells (which cannot be seen by direct observation) 

 appears to retain the spores for some time longer in some- 

 what close proximity. 



Soon after the separation of the spores the formation of 

 the outer spore- membrane commences. The inner trans- 

 parent layer f is first visible (PL LV, fig. IV), and soon 

 afterwards the outer one also, which is composed of a quan- 

 tity of two different substances varying in their refractive 

 power. Both layers take part in the composition of the 

 long spines of the exosporium, which are united by reti- 

 culate ridges (PL LV, fig. 17). During their formation 

 the three converging ridges at the top of the spore become 

 somewhat more conspicuous ; each of them now appears 

 to be traversed by a fine longitudinal fissure. The spines 

 appear as slight projections of the inner glassy layer 

 (PL LV, fig. 13), and gradually increase in length. When 

 quite ripe they appear considerably shorter than when 

 half-developed. It would seem that the pressure which 

 the rapidly -growing spores exert upon one another breaks 



* In some cases I was convinced that this cell floated almost in the middle 

 of the macrosporangium. At the time when one of the free spherical cells be- 

 comes (by division into four) the mother-cell of the spores, the free spherical 

 cells no longer entirely fill the inner cavity of the macrosporangium ; a space 

 filled with watery fluid is found above the place at which the stalk is attached 

 to the capsule. 



f Under transmitted light this layer is at first as clear as glass, then straw- 

 coloured, and ultimately brown. 



