279 
Cytology of Pythium ultimum , n. sp . 
branch suddenly made its appearance, immediately below the 
oogonium, and thirty minutes later, as shown in Fig. 3 e y the 
antheridium was fully formed. Nearly the whole of the re- 
mainder of the protoplasm in the aborted oogonium was used 
up in the formation of the antheridium. It is noteworthy 
that the oogonium occupies a terminal position until the 
antheridium is formed, when it is forced into a lateral one, 
a phenomenon common enough in cymose growths of very 
different kinds. Such displacements, combined with eccen- 
tricities of behaviour induced by the manipulation of the 
preparations, make continuous observations very tedious, and 
often practically impossible. The details of fertilization can- 
not be followed in organs orientated as in Fig. 3 e. Fig. 4 
gives the result of a study of the maturation of the sexual 
organs and of the process of fertilization. The oogonium 
represented in Fig. 4 a was placed under observation and 
watched until, at about 7.55 a.m.,the antheridial branch made 
its appearance. It was kept under constant observation until 
3.0 p.m. and drawings made at frequent intervals. It would 
serve no useful purpose to describe in detail the changes 
observed from time to time in the protoplasm, for we appear 
to have no clue to their significance. It would be just as 
unprofitable as to describe the different shapes assumed by 
an Amoeba. The figures represent all that is of interest in 
the present state of our knowledge. We note that the 
appearance of the protoplasm in the oogonium changes con- 
siderably during the first three hours. Denser patches appear 
and disappear. The differentiation of the oosphere does not 
take place in the manner described by De Bary for Pythium 
gracile y or by Ward in the species investigated by him. 
Further, there is no differentiation of gonoplasm and peri- 
plasm in the antheridium. 
The denser protoplasm, including all the particles of re- 
serve material, migrates towards the centre of the oogonium, 
leaving behind for a time an inconspicuous, faintly granular 
layer between it and the wall of the oogonium, as shown in 
Figs. 4 e and 4 /. De Bary and his followers regarded the 
