364 
WM. H. WESTON 
while another form seemingly identical should just as persistently 
fail to produce these organs. The physiologic investigations begun 
by Klebs, and carried on by a number of others, have gradually re- 
sulted in a far more enlightening conception of the family. Because 
of these investigations, we are, in the opinion of the writer, justified 
in regarding the Saprolegniaceae as a series of forms ranging from 
those which normally produce sexual organs, through forms which 
produce sexual organs only under unusual conditions, to forms which 
have entirely lost the power of sexual reproduction. 
On the basis of this ability to form sexual organs the Saprolegni- 
aceae may, for convenience, be divided roughly into three groups. 
First there are those forms which are strongly sexual producing an 
abundance of oogonia and antheridia even under adverse circum- 
stances. Here may be grouped Saprolegnia monoica de B., S. diclina 
de B., Achlya polyandra de B., A. prolifera de B., and others. Second, 
there may be grouped together those forms which possess the power of 
sexual reproduction, and perhaps even show a sexual stage as a normal 
phase of their life cycle under unknown conditions of growth in 
nature, but which under investigation remain imperfect; because the 
exact conditions favoring sexual reproduction are not supplied. 
Here belong Achlya oidiifera Horn, A. paradoxa Coker, Saprolegnia 
Kauffmaniana Pieters, and others. Finally, there are certain forms 
which have lost the power to produce any sexual organs whatever. 
The Achlya that is the subject of this paper, the Saprolegnia no. 66 
of Pieters, as well as other forms not as yet recognized as imperfect, 
should be placed in this category. 
The statement that these fungi are absolutely incapable of sexual 
reproduction cannot be made logically, of course, until they have been 
grown under every possible condition. Even if these forms should on 
later investigation be found to possess latent powers of sexual repro- 
duction, it seems probable that the category of non-sexual Sapro- 
legniaceous forms will still persist. It has long been recognized that 
the male reproductive organs or antheridia are invariably developed 
in some Saprolegniaceous species, occasionally in others, and never 
in some. In the genus Saprolegnia particularly, one can trace all 
gradations from forms normally developing antheridia in abundance, 
through forms in which antheridia occur rarely but may be induced, 
to truly parthenogenetic forms. In the opinion of the writer, a quite 
similar condition also obtains with regard to the oogonia of the Sapro- 
legniaceae. 
