85 



nucleus only is again seen. The most natural interpretation of 

 this is, that a nucleus passes over from the fertilising tube into 

 the oosphere and fuses with the central nucleus. I have not 

 been able to observe these phenomena directly, however, and, 

 therefore, I think the question as to whether fertilisation does 

 or does not take place is at present an open one. 



The nuclei in the oosphere, at all stages except the earliest, 

 appear to contain very little chromatin, and are very diflFerent 

 in appearance from the other nuclei. I may, however, point out 

 here that observations on the protoplasm and nuclei inside the 

 wall of the fully formed oosphere are rendered somewhat difficult 

 on account of the thickness of the cell wall, which prevents the 

 proper penetration of the preservative and other fluids. 



•At a late stage in the formation of the oosphere, the 

 antheridium contains only a very small number of nuclei. It 

 appears that some of them pass into the fertilising tube and 

 then into the periplasm, through the breaking down of the 

 swollen end of the tube, which disappears altogether at a later 

 stage, the smaller portion of the tube also becoming lost to 

 view. 



The outer layer of the wall of the oospore is formed by the 

 deposition of the whole remaining mass of protoplasm and nuclei 

 upon its inner wall in the form of a rugose mass which gradually 

 becomes converted into a dense exosporium. The wall of the 

 oogonium at the same time contracts and forms at this stage a 

 much crumpled and more or less disorganised envelope for the 

 oospore. The antheridium also contracts and finally disappears 

 altogether. 



When mature, the oospore contains a considerable quantity of 

 oily substance which is generally found in the centre, surrounded 

 by a layer of granular protoplasm. It now enters upon a period 

 of rest which probably lasts until the following spring, when it 

 begins to germinate. In the different species of the group this 

 germination varies. The oospore enlarges and bursts the exosporium 

 and the inner portion sends forth a tube which may at once 

 develop into a new plant, or it may produce a sporangium in 

 which are formed motile spores, each capable of germinating and 

 producing a new individual. 



The formation of oospores appears to depend to some extent 

 upon the nutriment available. During the summer, when the 



