No. 460.] STUDIES ON PLANT CELL. V. 235 
18, b) but the form of the sperm can be recognized fora long 
time. The chromatin of the egg nucleus is in a resting condi- 
tion at this period and the densely packed mass of paternal 
chromatin is very conspicuous in the loose, delicate network of 
the female chromatin. The mitosis following fertilization does 
not occur for several days so that it is not easily studied and 
the organization of the first cleavage spindle with the history of 
the maternal and paternal chromosomes has never been followed. 
But it is clear that we have in the pteridophytes a true fusion 
nucleus containing for several days both maternal and paternal 
chromatin within the same nuclear membrane. 
There is only one paper that gives any details of fertilization 
in the bryophytes, a contribution of Kruch ('90) on the liver- 
wort, Riella, which seems to have been generally overlooked in 
recent literature. After the sperm enters the egg, a male 
nucleus is organized which increases in size until it is about 
equal to the egg nucleus. The chromatin in both gamete nuclei 
is described and figured as forming 8 chromosomes which are 
organized before the fusion. The two gamete nuclei were 
observed, but not figured, in contact and it was not possible to 
distinguish in size the male from the female. This account is 
then very different from those of the pteridophytes since the 
sperm nucleus does not enter the egg nucleus but the two fuse 
side by side and with their chromosomes fully organized. There 
are, however, some points in Kruch’s paper that require more 
extended investigation and confirmation in the light of modern 
research. 
There is left only the group of the thallophytes where less is 
known about the detailed behavior of the chromatin during fer- 
tilization than in any region of the plant kingdom. The conju- 
gation of the gamete nuclei has been observed in a number of 
thallophytes, representing all of the higher groups. All of the 
authors, with the exception of Chmielewski ('90 b) for Spirogyra, 
describe the product of conjugation as a fusion nucleus, 7. e., 
one in which the nuclear substance of both gametes is con- 
tained within a common nuclear membrane. The most detailed 
accounts of the fusion of gamete nuclei in the thallophytes are 
those for Fucus (Strasburger, 97a; Farmer and Williams, ’98). 
