SCHISTOSTEGA OSMUNDACEA MOHR. 371 



this chloroplast appears to enlarge by subsequent growth until it 

 assumes a plate-like form, when it divides to form the " rosette " 

 shape (Plate 24, fig. 6). In Plate 24, fig. 3, cell number 3 will 

 be seen to contain a single " rosette " bowl-shaped chloroplast 

 and several unassociated and irregularly shaped chloroplasts, 

 one of which will pass into the new light- cell seen to be in process 

 of forming at A. The light-cell with the " rosette" chloroplast 

 is undoubtedly the ideal cell of the system, but the " rosette " 

 shape is not always produced, it is frequently replaced by 

 irregularly shaped chloroplasts which are also bowl -shaped. 

 Cell 13 in fig. 3, Plate 24, shows a frequent type of irregular chloro- 





Fig. 5. 

 CiaqTam of \\g\\i rays in ob-coiiicai cell. 



(After Noli.) 



plast formed of four roughly triangular portions with their 

 apices forming the bottom of the bowl. In som^e cases numerous 

 large circular chloroplasts aggregate in an irregular manner at 

 the bottom of the cell, but whether these combine and eventually 

 form a " rosette " I have not been able to determine. It is, of 

 course, these cells that produce the peculiar luminous appearance 

 for which Schistostega is knovv^n, and Noll gives the following 

 explanation (19) — " The rays of light which fall upon the cell are 

 refracted and concentrated upon the chlorophyll grains. Owing 

 to the shape of the cell the rays are totally internally reflected from 

 the basal walls of the cells and are again emitted, which gives the 



