Cytology of a new variety of A chly a americana. 135 
times was the endeavour made to get rid of the spiny form, 
and in each case control-cultures were set up. The number 
of spiny oogonia certainly seemed to decrease, but they 
did not disappear. It was a source of much gratification 
later to discover oogonia of both kinds on one and the same 
filament grown under microscopic control in a moist chamber. 
It is possible that the decrease in number in the later genera- 
tions was due to the process of selection I adopted. The 
infecting material used in these experiments was a single 
hypha bearing smooth oogonia. 
The result of a long detailed study of the systematic 
position of the form under consideration leads me to conclude 
that it comes very close to Achlya americana , a species first 
recognized and described by the late Dr. Humphrey (’ 92 ) 
in his monograph on the Saprolegniaceae of the United 
States. It presents, however, several important points of 
difference, which it is not likely that Humphrey could over- 
look. In any case it needs accurate definition, especially 
in view of the controversies which seem to be inevitably 
associated with work on this group of plants. I propose 
to rank it provisionally as a distinct variety under the name 
Achlya americana (Humphrey), var. cambrica. The specific 
and varietal names will thus serve to call attention to one 
important feature in connexion with the plants— their geo- 
graphical distribution ; and the detailed description will not 
only serve to prevent misconceptions as to the nature of 
my raw material, but it will enable those botanists who are 
familiar with Humphrey’s plant to relegate the forms to their 
true systematic positions. 
The following is a detailed description of this variety 
Achlya americana (Humphrey), var. cambrica, var. nov. 
Mycelium, as developed on house-flies, with main hyphae about 
1 cm. long, a maximum diameter at the base of 92 > u, and tapering 
gradually towards the apices, where they rather suddenly narrow to 
fairly sharp points. 
