590 Wager. — The Sexuality of the Fungi . 
Again, in Peronospora effusa the sexual organs are found in 
abundance in the leaves of the host-plant, but always in 
greater abundance in the young leaves near the apex. Also 
in Peronospora Arenariae , which is found upon many of the 
Caryophyllaceae, I soon found that it was useless to look for 
sexual organs in those parts of the plant which are covered 
with a luxuriant growth of asexual organs, but that they were 
only to be found in certain parts of the stem which were 
slightly differently coloured from the rest, and on which 
asexual organs were not found in any quantity. 
Hartog strongly supports the rejuvenescence theory 1 . He 
brings forward a considerable body of evidence to show that 
replacement theories of fertilization are inadmissible, since 
all fail to account for one or more of the many phenomena 
involved in the various types of sexual fusion of nuclei. He 
points out that rejuvenescence is brought about by(i) change 
of the mode of life, (2) plasmodium-formation, (3) isogamy, 
involving the fusion of two or more gametes and their nuclei, 
and (4) oogamy. He further points out that many cases of 
parthenogenesis involve the fusion of sister nuclei, and that 
this ‘ replaces the advent of a male nucleus.’ Among the 
Fungi he instances Saproleg?iia as a case in which this occurs, 
but this requires confirmation, as does also the case of 
Sporodinia described by Leger 2 , in which he describes the 
same phenomenon as occurring in the formation of the 
azygospores. 
In animals the polar bodies formed during the maturation 
of the egg are now generally regarded as reduced ova, or, as 
Hartog says, they represent true gametes arrested in their 
development. In certain cases the second polar body remains 
in the egg, and Boveri discovered ‘ that in Ascaris the second 
polar body might in exceptional cases remain in the egg, and 
there give rise to a resting nucleus indistinguishable from the 
egg-nucleus or sperm- nucleus.’ He was thus led to the 
interesting suggestion that parthenogenesis might be due 
1 Hartog, Some Problems of Reproduction, Q. J. M. .S., 1891. 
2 Leger, loc. cit. 
