Dr. C. A. Koloid on PlcoiJoriria illinoiaensis. 145 



many cells a faintly marked notch or furrow (/m., fig. 1) is to 

 be (leteett'tl on one side of tlie eliritniatophorc at the anterior 

 end of the cell. This seems to mark the line of contact of 

 tiie sides of the chromate>pli()re which has surrounded the 

 nucleus. In the 2- and 4-cell stages of the gonidial cells 

 the nucleus and the protoplasmic mass are jdainly seen 

 to occupy one side of the cell (PI. VI. figs. 7, 8), but in 

 the cells of the young colony it again oeeupies a central 

 position. 'IMie ehromatophore is uniforndy of a bright ehloro- 

 jhyll-^reen, and shows a tinely granular structure under high 

 magnification. In the youngest colonies each cell contains 

 but a single sjdierical pyrenoid (;^y.), which occupies a lateral 

 position in the ehromatophore, in the iinier hemisphere of the 

 cell. In the older colonies the number of jjyrenoids increases, 

 as many as twelve having been found. They are scattered 

 irregularly throiigh the ehromatophore, and may occur in any 

 part of it. A similar increase of pyrenoids is reported by 

 Shaw (1894) for P. californica. In the vegetative cells the 

 number of ])yrenoids is often but 2-4, and is, as a rule, less 

 than tliat t>f the gonidial cells. In a very icw instances as 

 many as eight have been found, and in one old colony the 

 vegetative cells seemed to be packed full of pyrenoids. In the 

 young colonies the pyrenoids have a diameter of about 1 /i, 

 and in the older colonies of 2 5/jl. 



The nucleus («.) lies in about the centre of the cell in the 

 midst of a mass of protoplasm enclosed by the ehromatophore. 

 In mature gonidial cells before division it has a diameter of 

 7-8 fi, and contains a sub-central nucleolus (ncl.) whose 

 diameter is 3 fi. The nucleolus stains deeply with picro- 

 carmine, and is by this means easily distinguished from the 

 pyren'oids, which it resembles in appearance and size. The 

 imclear membrane is detected with ditliculty. It encloses a 

 faintly stained nuclear reticulum (r.). In the younger cells 

 the nucleus is nmch smaller (4-a /i), the nucleolus is rela- 

 tively larger, and the reticulum is not evident. In the living 

 cell the nucleolus alone can be seeu in the midst of the 

 greyish protoplasmic mass at the centre of the cell. The 

 protoplasm is continued from this central region peripherally, 

 ill the axis of the cell as a slender column (/>.c.), to the 

 anterior end, where it includes the stigma and bases of the 

 two tlagella. A protoplasmic mantle enclosing the chrouiutj- 

 phore was not demonstrated. 



The stigma or eye-spot (s.) lies at the anterior end of the 



cell, near its axis, and is often so placed that an etiui lateral 



triangle may be drawn with it and the bases of the two llagolUi 



as apices. It is of a bright reddish-brown colour, though in 



Atin. d: May. A'. I list. S.r. 7. Vol. vi. lU 



