1910) BROWN—NUCLEUS AND CYTOPLASM IN PEPEROMIA IQI 
(BROWN ’08). It is not necessary to assume that the process is a 
simple chemical precipitation, because it may be a physiological 
response. 
The question now arises as to what happens when the nuclear 
membrane disappears during prophase. In Peperomia sintenisii 
the incipient spindle fibers form a dense felt over the nucleus before 
the membrane disappears. The appearance of spindle fibers before 
the disappearance of the nuclear membrane has been described in 
Lilium, Podophyllum, and Helleborus (MorTrTiER ’97), Equisetum 
(OsTERHOUT ’97), Cobea and Gladiolus (Lawson ’98, ’00), Pellia 
and Anthoceros (Davis ’99, ’01), Lavatera (BYXBEE ’09), Osmunda 
(SMITH ’00), Larix (ALLEN ’03), and a number of other genera. 
In Peperomia sintenisii, as in a number of other forms, the appearance 
of the cytoplasm around the nucleus is at this stage quite different 
from what it was before the appearance of the fibers, and the dis- 
appearance of the membrane may be connected with this change of the 
cytoplasm. 
When the cytoplasmic vesicle in Peperomia sintenisii becomes 
nucleoplasm, the question arises as to whether the cytoplasm has 
passed into the nucleus and nucleoplasm into the vesicle, or whether 
the cytoplasm is changed while in the vesicle. If, as seems probable, 
the nuclear membrane is formed by the interaction of the nuclear 
sap and the cytoplasm or some part of the cytoplasm, it seems evident 
that that part of the cytoplasm which participates in the formation 
_ of the membrane could not pass through the membrane, because, 
if it did, on coming into contact with the nucleoplasm it would only 
thicken the membrane. This does not mean, however, that no 
substances can pass from the nucleus to the cytoplasm or from the 
cytoplasm to the nucleus. It seems evident, however, that in Pepero- 
mia sintenisii the cytoplasmic vesicle, on account of its position, 
is converted into nucleoplasm through the activity of the nucleus, 
for there is no more reason for thinking that this part of the cytoplasm 
would change itself than there is for thinking that all of the cytoplasm 
would do the same thing. Then since the cytoplasm cannot pass 
unchanged into the nucleus, it is probable that some substance passes 
out into the*cytoplasm and changes the cytoplasm in such a way 
that it may then be taken into the nucleus. It is not likely that 
