88 BOTANICAL GAZETTE [AUGUST 
THEORETICAL CONSIDERATIONS. 
The essential agreement of the processes of oogenesis in Vaucheria 
with those of Saprolegnia and members of the Peronosporales is 
most striking. The oogonium in all of these forms so far known— 
Vaucheria, Saprolegnia, Pythium, Peronospora, Plasmopara, Sclero- 
spora, Albugo, and Araiospora (KING ’03)—is differentiated from 
the parent filament as a multinucleate cell. There may be one 
mitosis in the oogonium (Saprolegnia), or two as in certain of the 
Peronosporales, or there may not be any (Vaucheria), but finally 
extensive nuclear degeneration always begins. From among the 
weakened nuclei one or more are selected to preside over the eggs. 
The position of these surviving gamete nuclei in relation to favorable 
dynamic centers of the oogonium determines their selection and leads 
to extensive regenerative growth. In Saprolegnia and some of the 
Peronosporales (i. ¢., Albugo, Peronospora, Plasmopara, Sclerospora) 
the dynamic centers are marked by the protoplasmic structures 
called coenocentra, which are apparently trophoplasmic in character, 
since they exert a chemotactic influence on the gamete nuclei near 
them and are obviously concerned with their later growth. Although 
there is no coenocentrum in Vaucheria, the surviving nucleus takes 
its position in a central mass of protoplasm which is evidently the 
most favorable situation in the oogonium for its growth, and as such 
1s a dynamic center, although there is little morphological evidence 
of the condition. 
The fact that there are no mitoses in the oogonium of Vaucheria 
18 Seriously against the view that they have relation to reduction 
phenomena when present in the oogonia of Saprolegnia and the Per- 
Onosporales. I have already expressed the conviction (DAVIS "03s 
PP: 339-342) that these mitoses in the oogonium have no such signifi- 
| een are so variable in their appearance << er 
a. ase oe evidence of such functions. ROSEN nee ( le 
che thet of thc oo believes that a synapsis condition me si 
form indicates ~ cas = oem ay aad del apg ee tetrad 
division of the « uction phenomena comparable to that in the ae 
. Pore mother-cell of higher plants. The author 
Tree < : : 
Fespects, which need not 
be repeated here, and the absence of mitoses — 
e 
