234 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



force, cannot resume its normal rate of growth if, indeed, 

 it may be said to have any one normal rate, though it must 

 and does have normal rates. 



VII. Nucleus or Pyrenoid as the Central Body of 

 Cystococcus Cells. 



There remains one more point to be discussed in this 

 paper. In two papers which I have been unable to see but 

 which are briefly reviewed in Just's Jahresbericht (Bd. 

 XXII, I, p. 148), Dangeard (1894) claims that the body 

 generally regarded as the nucleus of gonidial cells is not 

 nucleus at all but a pyrenoid, the real nucleus being at 

 the side, small, inconspicuous, and formerly supposed to 

 be a vacuole. Differential staining agents are alleged to 

 prove Dangeard's assertion. As the species of gonidia 

 investigated by Dangeard are not mentioned in the review, 

 I cannot criticise his results and can only advance evi- 

 dence to show that the central body in the cells which 

 serve as the gonidia of the lichens reported upon in this 

 paper, is certainly a nucleus, as the well known nuclear 

 stains and the phenomena of division and cell-division 

 plainly indicate. In a spherical cell, too, one would cer- 

 tainly expect to find the nucleus near if not at the center of 

 the cell under ordinary conditions. In no case have I found 

 a nucleus-like body far from the center of the gonidial cells 

 of the lichens which I have studied. One would expect the 

 nucleus to have the size in proportion to the diameter of the 

 cell which this central body possesses, and not to be small, 

 eccentric and inconspicuous. The form of the nucleus 

 would be likely, for mechanical reasons, to approach that 

 of the cell, though of course this is by no means always 

 the case even in spherical cells. Pyrenoids occur always 

 in chromatophores, as specially differentiated parts of them, 

 not as independent organs. 



In fig. 16 we have a typical gonidial cell in a thin micro- 

 tome section of R. reticulata, stained on the slide with 

 Iodine- green -Fuchsin. The central body, enclosed in 



