142 Murphy.—The Morphology and Cytology of the 
General Considerations. 
The results of cytological investigations on the Oomycetes have been 
so much discussed that it is not proposed here to do more than present 
a short summary of the more recent work. It would serve no useful 
purpose to recall now forgotten controversies that waged round the question 
of the presence or absence of nuclei or of fertilization in the Saprolegniaceae. 
Even the pioneer work of Wager up to 1900 may be passed over because 
all the forms he worked with have since been reinvestigated by himself or 
by others. The same may be said of Trow’s earlier researches on the 
Saprolegniaceae, and of Berlese’s work on the Peronosporaceae. 
The modern period for us begins with Stevens’s paper on Albugo Bliti 
in 1899 ( 34 ). Further papers by the same author (35 and 37 ) deal with 
A. Portidaccie , A. Tragopogonis , A. Candida and A. Ipomoeae-Panduranae . 
Davis ( 14 ) investigated A. Candida again and Kruger ( 22 ) reinvestigated 
the same species in 1910. Finally Ruhland ( 32 ) worked on A. Lepigoni , 
which completes the list of work done on that genus. 
Turning to the genus Pcronospora , the first work of which we shall 
take account is Wager’s ( 42 ) on P. parasitica. Ruhland ( 32 ) reported work 
on P. Alsinearum , P. affinis, and P. Violae; and Kruger ( 22 ) investigated 
P. Ficariae. 
Two species of the genus Plasmopara have been examined : P. alpina 
by Rosenberg ( 31 ), and P. densa by Ruhland ( 32 ). 
Sclerospora has been investigated by two authors also: Stevens ( 36 ) 
worked on an unnamed species, and Ruhland ( 32 ) investigated S. gramini- 
cola. 
Trow ( 40 ) and Miyake ( 24 ), both in 1901, examined Pythium , the 
former P . ultimum , and the latter P . de Baryamim. 
The work done on the Saprolegniales is given only passing reference 
and will be just enumerated here. Trow ( 39 ) worked on Achlya americana , 
and later ( 41 ) on A.polyandra , Hildebrand, and A.de Baryana , Humphrey. 
Mucke in 1908 ( 25 ) reinvestigated A. de Baryana , Humphrey, under the name 
of A. polyandra, de Bary. Davis ( 15 ) worked on Saprolegnia mixta in 
1903, choosing an apogamous form ; and Claussen (8) investigated 
S. monoica. The list is concluded with the work of King (20, 21 ) on 
Araiospora ptdchra , one of the Leptomitaceae. 
Even in the field of cytology it would be difficult to parallel the diversity 
of findings and of conclusions of these authors. Thus in the case of Albugo 
Candida^ which has been examined three times since 19CO, Davis ( 14 ) found 
that there was one division in the oogonium, that the ooplasm was for 
a time nucleus-free, and that there was an organized coenocentrum. 
Stevens ( 35 ) found two divisions in the oosphere, which was never nucleus- 
free and contained a coenocentrum with inclusions and attractive functions. 
