6io Trow . — The Karyology of Saprolegnia . 
menced in ’51 and terminated in ’83) not only made us well 
acquainted with the whole course of development in a con- 
siderable number of species of Saprolegnieae, but placed the 
taxonomy of the whole group for the first time on a satis- 
factory basis. The method adopted by De Bary of cultivating 
each species separately for many generations — that of so- 
called 6 pure cultures ’ — has been of inestimable value. 
It may be useful to briefly refer to those features in the 
structure and life-history of the Saprolegnieae which were 
placed beyond doubt mainly by the labours of these two 
great pioneers. 
In the Saprolegnieae the mycelium is branched, unicellular 
and multinucleate,— or to use Vuillemin’s term, — apocytial. 
Certain branches — the rhizoids — penetrate the nutritive sub- 
stratum and serve to absorb nourishment from it ; other 
branches, when fully developed, bear the reproductive organs. 
These are, with rare exceptions, of two kinds — asexual and 
sexual. The asexual organs are sporangia, and give rise to 
numerous biciliate zoospores. The sexual organs — oogonia 
and antheridia — are produced in considerable numbers. 
Oogonia have been found in nearly all the species, and it is 
by no means improbable that they occur even in those few 
species in which their presence has not, so far, been noticed. 
The antheridia may, according to the species, be always 
absent from the oogonia, always present on the oogonia, or 
present on some of the oogonia and absent from others. 
The antheridia are generally borne on special antheridial 
branches. When these branches arise near the oogonium the 
species is said to be androgynous , and when at some distance 
from the oogonium, diclinous. 
It is especially noteworthy that in two species only — Achlya 
stellata and Saprolegnia monilifera — have the oogonia been 
found to be invariably destitute of antheridia. The closely 
related species or races — .S', mixta , S. tomdosa , and .S'. Thureti 
— have a certain but variable number of oogonia with anthe- 
ridia attached to them. In cultures of S. mixta S°°/ 0 °f the 
oogonia bear antheridia, in cultures of .S', torulosa antheridia 
