300 BOTANICAL GAZETTE [APRIL 
of mercury, while a pressure of over 15,000™™ is necessary to bring about a 
marked response in the alga.2 Perhaps there is a stimulating chemical 
in sea water which aids the somewhat high osmotic pressure to bring about 
the result. At a dilution of one-thousandth the filaments grow normally 
as in weak nutrient solutions. 
The result of this test suggests how a fresh-water form coming into sea 
water may be influenced to change its character and still live and thrive. 
This may have been a factor in the evolution of certain algal forms.— 
Burton Epwarp Livincston, The University of Chicago. 
FERTILIZATION IN THE SAPROLEGNIALES. 
Proressor B. M. Davis, in his criticism of my views ‘‘On fertiliza- 
tion in the Saprolegnieae,” makes use of the term ‘“‘ovocentrum” in a 
sense very different from that which I gave to it. His use of the term, 
moreover, is obviously based on a misconception of my meaning. He 
says ‘‘Trow calls the egg-asters ovocentra.” I neither do this, nor do 
I approve of it being done. Such an innovation would be worse than 
useless, as it would increase the confusion which already exists. At present, 
unfortunately, structures of more than one kind have apparently been 
grouped together by giving them a common name—‘“coenocentrum.” I 
suggested the term “ovocentrum” as suitable for use in describing the 
dense mass of protoplasm found at the center of the eggs of the Sapro- 
legnieae. Imbedded in the ovocentrum of an egg I find a single nucleus 
accompanied by a single centrosome and its astrosphere. It would have 
been correct, I think, for Davis to have said that the “coenocentra” dis- 
covered by him in Saprolegnia were interpreted by me—rightly or wrongly 
—as consisting of centrosomes with their astrospheres. The “ovocentra 
of the Saprolegnieae may be the equivalents of the coenocentra of 
Peronosporeae. They are altogether different from centrosomes and as 
spheres. I cannot, therefore, accept DAvIs’s statement that I call “the ese- 
asters ovocentra.’’ I do not propose to discuss the many other points of 
interest raised by Professor Davis, for new facts are required now, and 
these can only be obtained by patient and prolonged investigation 19 a 
laboratory.—A. H. Trow, Cardiff, Wales. 
8 Loc. cit. (1) and (2). 9 Bor. GAZETTE 39:61. 1995. 
tro- 
