370 G. T. HARRIS ON 



arranged principally on each surface of the cell wall (Plate 24, 

 fig. 2). As the distichous leaves of the adult plant are set vertic- 

 ally on the stem, and as the stem grows usually at right angles to 

 the incident light, the edge of the chloroplast is consequently 

 presented to the action of light, though it would seem that a 

 certain amount of translocation takes place, as many of the 

 ■chloroplasts may be seen ranged along the side walls of the cells, 

 in which position the whole surface of the chloroplast would be 

 exposed to the action of light. 



The light-cells themselves are obconical in shape and of about 

 30/Jt X 20/>t when at their maximum growth. They are produced 

 from the end of a filament by a process of budding, and as previously 

 mentioned they often assume a more or less regularly pinnate 

 growth, and form a superficial aggregate of considerable size. 

 They may on the contrary be sparingly developed and scattered 

 singly or in small groups among the filaments. The distal portion 

 •of an ordinary linear cell becomes swollen and the chloroplasts 

 ■become much enlarged, the next cell in series, produced by 

 budding, is shorter and more globular ; eventually the cells become 

 quite globular and assume the ideal obconical form. Lateral 

 bidding takes place later until eventually the superficial aggregate 

 is^^formed, Plate 24, fig. 3. The chloroplast of the ideal light-cell 

 is bowl-shaped and fills the conical bottom of the cell to about 

 one-third of its height as shown in fig. 4, Plate 24, where the 

 obconical cells are shown in vertical section. Bowl-shaped 

 <5hloroplasts are of frequent occurrence in the genus Anthoceros 

 i( Liver worts), they also occur in Selaginella martensii, but they 

 probably are nowhere developed to such a state of efficiency as in 

 the photo-synthetic system of Schistostega. In its most perfect 

 form, which may be described as the " rosette " form, it consists 

 of six wedge-shaped chloroplasts arranged in a circle around a 

 seventh, which is central and lies at the bottom of the obconical 

 oell. This ideal " rosette " chloroplast is seen in cell 5, fig. 3, 

 Plate 24. It will be seen that a highly efficient photo-synthetic 

 -cell is produced by the obconical shape with the bowl-shaped 

 ■chloroplast filling the conical base, their separate pieces so arranged 

 as to present a uniform sheet of chlorophyll to the light condensed 

 .-by the convex portion of the cell. On the budding of a new light- 

 •cell from a parent cell one or more chloroplasts pass into the new 

 J3ud before it is separated from the parent (Plate 24, fig. 5), and 



