1895.] Anatomical and Physiological Researches. 223 
fore him, that masses of nucleolar substance may sometimes 
be seen in the cytoplasm during karyokinesis. But this au- 
thor attempts to show that the nucleoli are characteristically 
thrown out of the mother-nucleus into the cytoplasm during 
division, to be reabsorbed into the daughter-nuclei. The 
present reviewer (9) has attempted to show that this extru- 
sion of nucleolar substance is not constant, nor even com- 
mon, in any plant studied by him; and Guignard has found 
(7) in Pstlotum triquetrum that the frequence of the phe- 
nomenon depends, in the sporogenous tissue, upon the stage 
of its development. The writer can see nothing in the be- 
havior of nucleoli to justify Zimmerman’s view of them as 
organs of the cell. Their indefiniteness in form, size, num- 
ber, and position in the nucleus, and their total disappear- 
ance in most cases during karyokinesis, all point to the 
conclusion that they are masses of substance subject to the 
activity of the nucleus and perhaps furnishing plastic mate- 
tial for certain cell-processes, to whatever parts of the cell it 
may be distributed while unrecognizable as nucleolar masses. 
And the fact that such recognizable masses sometimes occur 
in the cytoplasm affords no evidence that the whole of this 
substance passes normally into the cytoplasm when it disap- 
pears during karyokinesis. It is perhaps quite as probable 
that these masses represent a surplus which is not or cannot 
be disposed of in the usual way. 
The observation of nucleolar masses in the cytoplasm in 
Psilotum triquetrum led Karsten (10) to believe that they are 
the centrospheres, and that therefore, at least in this plant, 
the latter bodies are of nucleolar origin. The writer (9) has 
shown that this was due to his having quite overlooked the 
true centrospheres, a conclusion since entirely confirmed by 
Guignard (7). 
Since their first discovery in plant-cells by Guignard, the 
Centrospheres have been recognized with more or less cer- 
tainty by various investigators, so that their occurrence in most 
of the great groups of plants seems now assured. As has been 
intimated, the evidence is not equally satisfactory in all 
Cases that the structures regarded as centrospheres by the 
various writers have really been such. But, as it is practi- 
cally impossible to determine justly the merits of each case, 
it may suffice to give a systematic list of those plants in 
which they are claimed to have been seen, with the name of 
the observer in each case. 
