Trow,— The Karyology of Saprolegnia. 613 
apogamy of the Saprolegnieae has been generally accepted 
by botanists. 
It is only in recent years that the karyology of the group 
has received much attention. In addition to the researches of 
Schmitz (’79) and Strasburger (’80), special studies of the 
structure, behaviour, and fate of the nuclei in these plants 
have been made by Hartog (’89, ’91), Dangeard (’90 < 2 , ’90 
and ’91) and Humphrey (’92). 
Hartog (’91) states that the ‘nuclei are vesicles with 
a central chromatin-mass supported by a network of “ linin ” 
or nucleo-hyaloplasma.’ The nucleus of the zoospore is 
spherical and undergoes divisions by a process which is 
virtually direct, but nevertheless exhibits some features of 
karyokinesis. He (’89) also states that the division of the 
nucleus is preceded by great changes in the central mass of 
chromatin. This becomes very irregular and ends by dividing 
into two halves having the form of blunt crescents, placed back 
to back, and in structure distinctly ‘ fibrillaire.’ These crescents 
move away from each other (s’ecartent) and become spherical, 
and finally the nuclear wall is inflected so as to separate them, 
and thus the two daughter-nuclei are constituted. The nuclear 
divisions go on only in the mycelium and antheridia. No 
divisions consequently take place in the sporangia and 
oogonia. The number of nuclei which passes into a spor- 
angium is just sufficient to provide one for each zoospore. 
A large number of nuclei pass into the oogonia — many more 
than is sufficient to provide one for each oosphere. The 
vacuoles which form in the young oogonia bring these nuclei 
nearer to each other, and they fuse in pairs until, in the genus 
Saprolegnia , the number is reduced at the time of the forma- 
tion of the oospheres to one for each oosphere. Some of the 
details of the fusion are particularly interesting. £ In fusion 
of the nuclei the chromatin-masses long remain distinct, but 
are smaller and take up stain less readily (the italics are mine), 
and the nuclear wall at this stage ceases to stain, so that the 
fusion-nuclei have the look of vacuoles in the cytoplasm.’ In 
his last paper Hartog carefully distinguishes between these 
