634 Trow . — The K ary o logy of Saprolegnia. 
equally distributed in the protoplasm, and show no tendency 
even to come together in pairs, much less to undergo fusion. 
Development of the Antheridia up to the formation of the 
Fertilization-tubes. The antheridia have not been studied so 
thoroughly as the oogonia. The results won by the more 
difficult examination of the development of the oogonia, enable 
one to follow with ease the corresponding stages in the 
antheridia. Figs. 5, 9 and 10 show antheridia in successive 
stages of development. At the time of the separation of the 
antheridium from the antheridial branch by the formation of 
a basal wall, its protoplasm encloses a small but variable 
number of nuclei. These undergo division exactly as in the 
case of the nuclei of the oogonia. Fig. 8 c and d represent 
two nuclei from an antheridium. Degeneration of the nuclei 
certainly takes place in the antheridia at a very early stage, 
just as was seen to be the case in the oogonium. When the 
oospheres have been developed the antheridia give rise to 
the fertilization-tubes, and these apply themselves closely to 
the oospheres. 
Some of the small nuclei pass into these fertilization-tubes 
and are there specially easy to see ; others remain behind in 
the antheridium and ultimately degenerate, as indeed do many 
of those which pass into the fertilization-tubes. This later 
degeneration has been observed by many botanists, and has 
long been thought to furnish evidence of the absence of 
fertilization. 
Fertilization. The most detailed observations on fertiliza- 
tion were made on S', dioica , the species first studied, on 
sections stained with acetic-carmine. Early in the course of 
my investigations young oospores were found with two large 
nuclei, corresponding closely to those of Achlya americana 
figured by Humphrey. As the uninucleate character of the 
oospheres had already been placed beyond doubt, there re- 
mained but two alternatives to account for the presence of 
these two nuclei : they must have arisen either by the division 
of the pre-existing nucleus, or a new nucleus must have passed 
into the oosphere from some outside source. The structure 
