646 Trow . — The Karyology of Saprolegnia. 
periodic reduction of the chromosomes does not adequately 
explain the facts. So far as concerns the Thallophytes too, it 
may be safely asserted that his prophecies have not been 
fulfilled. He asserted, and at the time with sufficient justifica- 
tion, that ‘ the assumption that this reduction takes place 
during the development of the sexual organs is not supported 
by any direct evidence,’ and then proceeds to suggest that the 
necessary reduction takes place in the lower Cryptogams 
during the germination of the zygote. The facts already 
mentioned show quite clearly that a reducing division takes 
place in Saprolegnia , in the gametangia and not in the zygote. 
The great objection which all biologists must raise against 
Strasburger’s view is that <it necessitates one explanation of 
the reducing division in plants and another in animals without 
sufficient reason. Saprolegnia and most other Thallophytes 
(like animals) have no sporophyte-generation. If the real signi- 
ficance of the reducing divisions observed in higher plants is 
simply the return of the sporophyte-cells to their primitive 
gametophyte-condition, what meaning are we to attach to the 
corresponding process in Saprolegnia and animals where no 
such return is possible? It would needlessly complicate 
matters to assume that the zygote and its products constitute 
a sporophyte-generation in Saprolegnia , for they certainly 
do not ; and even if they did, no reducing division takes 
place in it. 
In plants in which there is no sporophyte-generation it 
would be reasonable to admit that the reducing division 
occurs, as in animals, in the sexual organs; and that the 
number of chromosomes is restored by the sexual act. The 
phenomenon consists essentially of a halving and a subsequent 
restoration to the whole condition, and this we have proved 
to take place in a characteristic manner in Saprolegnia . 
In plants in which there is a distinct sporophyte-generation 
there really appears to be no halving in connexion with the 
sexual process, but rather a doubling, and a reduction to the 
undoubled condition takes place in the transition from sporo- 
phyte to gametophyte. When we consider that the sporophyte 
