MUSCINE& HEPATIC JE MARCHANTIALES 



35 



Fig. 7, A shows the nucleus of the mother cell under- 

 going the first division. The small size of the nuclei, and the 

 small amount of chromation in them, make the study of the 

 details of the nuclear division difficult here, and as there was 

 nothing to indicate any special peculiarities these were not 

 followed out. After the first nuclear division the daughter 

 nuclei divide again, after which the four nuclei arrange them- 



FIG. 7. Riccia tricho'carpa. A, Section of a spore mother cell undergoing its first 

 division, X6oo; B, section of young spore tetrad, X3oo; C, section of ripe spore, 

 X30o; D, surface view of the exospore of a similar stage, X3OO. 



selves at equal distances from each other, the division walls 

 form simultaneously between them, dividing the spore mother 

 cell into the four tetrahedral spores. A section through such 

 a young spore-tetrad is shown in Fig. 7, B, where one of the 

 cells is somewhat shrunken in the processof embedding. The 

 cell walls at this stage are very delicate and of unchanged 

 cellulose ; but as they grow older the wall soon shows a separa- 

 tion into endospore and exospore. The latter in R. tricho- 

 carpa, which was especially studied, is very thick, at first 

 yellowish in colour, but deepening until when ripe it is black. 

 Sections parallel to the surface show in this species what 

 appear to be regular rounded pits, but vertical sections of the 

 spore-coat show that this appearance is due to a peculiar fold- 



