Pythium de Baryonum . 663 
Beriicksichtigung aller Merkmale begriindet 1st, passender, sie 
im Zusammenhang mit den S. zu besprechen, als besondere 
Familie, welche in der Mitte zwischen beiden steht.’ 
As remarked by Schroter, it is incorrect to base the 
classification solely on the mode of sexual reproduction. 
But the sexual organs are usually regarded as the most 
important characters used in classification, since the vegeta- 
tive parts of the plant-body are more liable to modification 
according to the conditions of environment to which the 
plants are subjected, while the reproductive organs undergo 
less change. The present studies show more definitely the 
close relationship of the Peronosporeae and Pythium in the 
mode of sexual reproduction. 
It appears therefore that its natural position would be in 
the order Peronosporeae rather than in the Saprolegnieae, 
although it occupies an intermediate position between the 
two. 
Summary. 
1. The mycelium of Pythium de Baryanum contains 
numerous nuclei irregularly distributed in the protoplasm. 
%. The young oogonium, which is formed as either a terminal 
or an intercalary swelling on the hypha, contains about 10 to 
15 nuclei. The nuclei are larger than those of the hyphae, 
and the chromatin granules are prominent in stained prepara- 
tions. 
3. The antheridium contains about 2 to 6 nuclei. The 
structure of the nuclei does not differ from that of the nuclei 
in the oogonium. 
4. The nuclei of the oogonium and antheridium undergo 
division previous to fertilization. The division is karyokinetic, 
and similar to that which takes place in Cystopus and Perono - 
spora. The formation of the karyokinetic spindle is intra- 
nuclear, and the nuclear membrane persists at least in the 
early stages of the division. 
5. After the division of the nuclei which were previously 
arranged near the periphery of the oogonium, the whole 
