559 
Trow . — On Fertilization in the Saprolegnieae . 
in all the other sexual species, can be traced up to the oospheres. With 
these they come into close contact — one which, once established, persists 
for a considerable time, and can be recognized even in fairly old oospores. 
It was the nature of this contact (see Figs. 2 6, 28, and 29), combined with 
the variation in the number of the nuclei, that led me, years ago, to look 
carefully for proofs of the entry of a sperm-nucleus. The fertilization-tube, 
after coming into close contact with one oosphere, generally sends out a 
lateral branch which may, and frequently does, come into contact with 
another oosphere. This fact, together with the failure to note the constant 
adhesion of the fertilization-tubes to the young oospore membranes, 
apparently led Hartog to regard the fertilization-tubes as functionless 
organs. A study of Figs. 23, 24, and 25 will suffice to show that the apex 
of the fertilization-tube not only indents the oosphere, but really penetrates 
into the ooplasm, and by virtue of the solution of its membrane allows a 
direct protoplasmic continuity to be set up between the fertilization-tube 
and the oosphere. The passage of a nucleus from the one organ to the 
other may be traced (Figs. 23, 24, 25, and 2 6). An admirable proof of 
the continuity of the protoplasm in both organs is furnished by Fig. 23, 
which may be interpreted as meaning that the nucleus is accompanied 
by an appreciable quantity of protoplasm — a gonoplasm is indeed de- 
monstrated. Such a figure reminds one very much of the nuclei squeezing 
themselves through the sterigmata of the Basidiomycetes, as figured by 
Ruhland (’ 01 ) in Hypholoma. Attention may be directed to one or two 
other points of interest. The protoplasm in the oosphere in the neighbour- 
hood of the fertilization-tube becomes more granular, stains more deeply, 
and acquires the character of a receptive spot. An elongated vacuole is 
often associated with the sperm-nucleus. In Fig. 25 this could be traced 
back into the fertilization-tube outside the oosphere. In Fig. 26, a case in 
which the fixing was not quite satisfactory, the vacuole-like structure 
occupies a tangential, not a radial, position. The limits of the cellulose cell- 
wall of the fertilization-tube at this time were not determinable with any 
degree of accuracy. The cellulose wall seems to stop short at the periphery 
of the egg, but the boundary between the ooplasm and the contents of the 
fertilization-tube is as represented in the figures, and gives the impression 
of a tube which penetrates some distance into the egg. Just at the time 
when the wall of the young oospore makes its first appearance, one fre- 
quently finds what appears as a prolongation of the fertilization-tube into 
the oospore in the form of a thimble-like vacuole (Fig. 28). 
These facts, taken by themselves, might still fail to satisfy sceptics as 
to the existence of fertilization in the Saprolegnieae. Fortunately, the 
close study given to the sperm-nuclei resulted in a very unexpected and 
apparently, so far as plants are concerned, a unique discovery. 
The centrosome and astrosphere of the male nucleus . The sperm- 
