102 FECUNDATION ; HETEROGAMETES. 
and Peronospora parasitica, fusion is retarded, taking place only 
after the egg has developed a tolerably thick wall about itself. The 
retarded fusion of the nuclei has already been pointed out for Spzvo- 
gyra, Cosmarium, Closterium, and Basidiobolus, and, as will be 
seen, it is of frequent occurrence in the plant kingdom. 
ACHLYA AND SAPROLEGNIA., 
The sexuality of the Sefrolegniacee is, perhaps, one of the oldest 
questions in botany still in dispute. The fact that apogamy obtains 
in so many species has led observers to accept with the greatest reserve 
any affirmation of sexuality, although based upon observations which, 
in other groups of plants, would not be questioned as positive proof 
of a sexual process. 
Pringsheim (’57) was probably the first to attribute to any represen- 
tative of this group a sexual reproduction, basing his conclusions chiefly 
upon a study of Saprolegnia monoica. He described the develop- 
ment of the sexual organs, the penetration of the oédgonium by the 
conjugation-tubes, and their growth inward among the egg-cells. He 
stated also that the tubes opened and discharged their contents among 
the eggs. Reasoning from the analogy of Vaucheria, Pringsheim 
concluded that a real sexual process existed in the species in question. 
Several years later De Bary (’81) combated this view, alleging that, 
as he did not observe the fusion of the conjugation-tubes with the egg- 
cells (Saprolegnia ferax and Achlya polyandra), no fecundation 
took place and that apogamy characterized the entire group. De Bary 
made a careful study of several species, keeping pure cultures of the 
same running for several years, and his view, it is safe to say, has been 
more generally accepted by botani$ts than that of Pringsheim. 
Pringsheim continued his studies, and in 1882 brought forth addi- 
tional evidence in support of his view. He described and figured the 
fusion of the conjugation-tubes with the egg-cells in Achlya polyandra, 
and, although his ‘* spermameeba”’ were nearly ameeboid parasites and 
not male gametes, as he persistently maintained, yet his collected 
observations seemed to furnish as strong evidence in favor of sexuality 
as that which could be brought against it by his opponents. Since the 
above mentioned publications of Pringsheim and De Bary the majority 
of observers dealing with the subject have leaned toward the view of 
De Bary. 
Within more recent years the subject has been taken up by Hartog 
(89, ’95) and Trow (’95, ’99), with the aid of improved technique, 
especially on the part of Trow. Hartog reaffirms the doctrine of 
