564 Humphrey . — On some 
of my former paper (’94) and Fig. 7 of the present one show 
some stages in its second division which yields the spore- 
cells. Not one of these shows any nucleolar substance in the 
cytoplasm ; nor does any in which the nuclear membrane 
is not intact show it within the nuclear cavity. It is not 
necessary to go into a detailed discussion of the matter, for 
Zimmermann has stated his position so uncompromisingly that, 
as Strasburger has said (’95), a single case of the solution 
and subsequent reappearance of the nucleoli during division 
overturns it at once. If the nucleolus is a definite organ, 
derived only from its like, it must persist as such so long as 
the cell is active. Zimmermann himself admits that he has 
not been able to see it in all cells with dividing nuclei in the 
apex of the stem of Phaseolus. I have seen hundreds of 
karyokinetic figures in cells of both vegetative and repro- 
ductive tissues of all the plants above named, which showed 
no trace of any substance reacting to stains like the nucleoli. 
Besides, when nucleolar globules are found in the cytoplasm 
they are as likely to remain there as to be taken into the 
nuclei resulting from the division. There is not the least 
indication of any provision for their return to a daughter- 
nucleus after being thrown out from the mother. (Cf. Fig. 2 
of my previous paper.) 
Strasburger (’95) finds that, in agreement with his earlier 
statements, the nucleolus in the pollen-mother-cells of Lilium 
usually becomes entirely dissolved at the time of the forma- 
tion of the spindle-fibres. And he adds that when a nucleolus 
is thrown out into the cytoplasm, this does not happen until 
it has been greatly reduced in volume, apparently by the 
solution of its substance. Guignard (’94) states, as a result of 
his study of Psilotum , that the persistence of the nucleoli is 
much rarer than their solution, and that the re-entrance of 
extranuclear nucleoli, when present, into the new nuclei is by 
no means a constant feature. In my examination of Psilotum , 
not a single well-marked case of extranuclear nucleoli was 
found. So far as the final divisions of the spore-mother-cells 
are concerned, Guignard found them almost equally rare ; 
