OEIGIN AND MORPHOLOGY OF CHLOROPHYLL CORPUSCLES. 247 



their simplest forms, as in marine Diatoms, and some Floridese, 

 these pyrenoids appear as small, round, highly refractive 

 granules, of -which one is found in each disc-like chrotnato- 

 phore. The structure is often complicated by the aggrega- 

 tion of numerous starch-granules round the pyrenoid. These 

 aggregations, together with the pyrenoids contained in them, 

 have long been known among green Algae under the terms 

 " chlorophyll vesicles," '' amylum bodies "i (Amyluraheerden, 

 Amylumkerne, Amylumkugeln) (figs. 16 and 17). Tlie 

 starch grains surrounding the pyrenoid may remain distinct, or 

 they may fuse laterally so as to form a continuous mass. The 

 number of pyrenoids, their arrangement and distribution in 

 the chromatophores, sometimes show great regularity ; in other 

 cases, and especially in large discoid chromatophores, there 

 seems to be no constancy in these respects. 



The pyrenoids themselves are colourless, spherical bodies, 

 consisting of a dense, highly refractive substance. This is a 

 point which it is difficult to observe ; when viewed under a low 

 power it appears as though the pyrenoids were more deeply 

 coloured than the rest of the chromatophore. But observation 

 with high powers shows clearly that they are colourless, dense, 

 refractive bodies embedded in the coloured mass of the chro- 

 matophore ; and this being the case, they ■would naturally 

 appear of a darker colour than the surrounding mass of the 

 chromatophore when viewed by transmitted light, and under a 

 low power. These colourless bodies appear to be homogeneous 

 when examined under high powers and in the living state. 

 Here again a reticulate structure appears under the action of 

 reagents, but Professor Schmitz is of opinion that this struc- 

 ture does not pre-exist. An investigation of the behaviour of 

 the pyrenoids before various reagents leads him to the con- 

 clusion, that the substance of which they are composed is, in 

 its chemical nature, nearly allied to that of the chromatin- 

 boglies (nucleoli) of the cell-nucleus, though at present it is 

 impossible to state definitely what the special nature of the 

 substance is. 



» Cf. Sachs, 'Text-Book/ 2iid Eagl. ed., p. 258. 



