No. 460.] STUDIES ON PLANT CELL. V. 235 



1 8, b) but the form of the sperm can be recognized for a 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, i. 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, '97 a; Farmer and Williams, '98). 



