34 PROrESSOR LANKESTER. 



average diameter of these discs was about the -^^th of an 

 inch and less. A series of them is represented in the plate 

 (Plate III), which gives a representation of a possible group 

 of these bodies (figs. 7 to 23), as obtained by teazing such a 

 film as that described. With a power of 600 diameters the 

 disc-like bodies are seen to vary both in colour and struc- 

 ture. Some are of' the very deepest ruby red (figs. 14, 28); 

 others are paler, but still of a rich colour (fig. 16) ; whilst 

 others, again (figs. 19, 20), have a decidedly brownish tint. 

 With the power of 600 diameters (Hartnack's No. 8 objec- 

 . tive and No. 4 eye-piece) many of the discs appear homo- 

 geneous, devoid of all granulation, and of gelatinous border 

 or capsule. This is the case equally with figs. 16, 17, 18, 

 19, 20, and 21. On the other hand, with the power named, 

 figs. 12 and 13 appear granular, and fig. 9 is seen to consist 

 of a closely adherent mass of plastids with a gelatinous 

 border. Fig. 15, again, is seen to have a relatively larger 

 amount of gelatinous matter separating its highly coloured 

 loculi (each of which corresponds to a plastid), whilst in 

 fig. 7 we have a form in which the primitive gloeogenous 

 sphere is breaking up into secondary spheres, each secondary 

 sphere containing numerous highly coloured loculi. 



When a higher power of the microscope is applied to these 

 discoid objects — namely, the No. 10 immersion of Hartnack, 

 with No. 4 eyepiece, giving an amplification of 1100 dia- 

 meters with the best definition and penetration which I know 

 of at that point of magnifying power — some of the 

 apparently homogeneous discs are resolved, and are found to 

 present a minutely punctate structure. Others resist the 

 test and still appear — as I conclude they are (within the 

 physical limits of the word) — homogeneous. 



Such homogeneous discoid plastids are represented in fig. 

 14, fig. 16, fig. 20, and in the series of smaller bodies to the 

 left of fig. 19. The most minutely punctate forms are seen 

 in figs. 18, 17, and 21. AVhen teased or broken by pressure 

 of the covering glass these discoid bodies give evidence of 

 being composed of a somewhat tough coherent substance, 

 and do not diffuse or break up into granules. 



The following is the explanation which I have to offer of 

 these appearances. Under certain conditions of growth, 

 which I have not been able to determine specifically, but 

 which are possibly amongst others those of diminished nu- 

 trition — the plastids of B. rubescens cease to multiply by 

 transverse division or to form filamentous or other irregularly 

 extended growths. They cease also to form gelatinous 

 envelopes and take on a physiologically homogeneous cha- 



