282 Trow. — Observations on the Biology and 
wall becomes distinctly two-layered, and as it grows older it 
acquires a yellowish colour. The so-called oil globule, better 
named reserve globule, develops in the middle of the proto- 
plasm, and lastly between the central globule and the wall 
a large nucleus makes its appearance. Fig. 5 shows successive 
stages in maturation in the case of an oospore which ripened 
very slowly. The egg was fertilized on 29/8/99 at about 
5 p.m. The oospore took more than three days to ripen. 
The following summary will serve to show roughly the 
time occupied by this species of Pythium in passing through 
the various stages of development : — 
For the growth of the mycelium . . .48 hrs. 
For the completion of the development of a 
half-grown oogonium , reckoning up to the 
first appearance of the antherial branch . 4I „ 
For the formation of the antheridium . . 30 to 45 min. 
From the complete formation of the antheri- 
dium to the commencement of oosphere 
differentiation ...... 2I hrs. 
From the commencement of oosphere differ- 
entiation to the first noticeable move- 
ment of protoplasm in the fertilization- 
tube (act of fertilization?) . . 2 „ 
From the act of fertilization to the rounding 
off and definite limitation of the oospore . 1 ,, (?) 
For the maturation of the oospore . . . 24 „ 
Ripe oospores may, as a matter of fact, be obtained in 
abundance on the fourth day in suitable cultures. Three- 
and four-day cultures would then be generally suitable for 
the preparation of serial stained sections, and were indeed 
most frequently used. 
Germination of the oospores. The oospores germinate as 
soon as ripe, or after a period of rest extending to seven 
months. The process of germination resolves itself into two 
stages, which are in my experience generally separated by 
a period of rest. In the first stage the oospore becomes a 
