Pethybiudge — Observations on Phytophthora erythroseptica. 189 



The early stages in geriuiuation consist of a passage in the reverse order 

 through the later phases exhibited during the ripening of the oospore. The 

 structure of the ripe oospore was described on pp. 186 and 187. When germina- 

 tion is beginning, the large central oil-drop loses its identity, becoming broken 

 up into smaller ones. The bright oval body disappears, the finely granular 

 peripheral protoplasmic layer becomes coarsely granular, and the oospore 

 becomes completely filled with what resembles a uniform but somewhat 

 coarsely granular emulsion. 



At this stage the thick wall of the oospore commences to be dissolved 

 from within outwards ; the rate of solution is not uniform all round ; and 

 hence the inner margin of this wall has now a more or less irregularly corroded 

 appearance. (See fig. 3, Plate XIII.) Finally the oospore wall is reduced 

 to the thickness of the outer layer alone, and is thus very slender. 



The dissolution of the greater part of the thick oospore wall in the 

 manner described strongly suggests that its function is not merely that of 

 protection during the resting period, but that it also acts as a reserve-supply 

 of food material ; and it may be observed that since the blue colour pro- 

 duced in it by the iodine reagents previously mentioned is quite different 

 from that produced in the antheridial and other walls, it seems fair to con- 

 clude that it consists of some special form of cellulose, which, however, is 

 not directly soluble in ammoniaoal copper hydrate solution. ^ 



A germ-tube arises from the now thin-walled oospore, penetrates the 

 oogonium wall, and so reaches the exterior, when it resembles an ordinary 

 hyplia. After growing in length to a greater or less extent, and frequently 

 producing branches, conidia (zoosporangia) are produced in some cases, in 

 others the germ-tube and its branches become ordiuai-y hypliae ; and in a 

 few days a considerable and complex mass of mycelium results. 



When the oospore completely fills the spherical portion of tlie oogonium, 

 the point of penetration of tlie oogonial wall by the germ-tube coincides 

 with the point of origin of the germ-tube itself from the oospore. (See text 

 fig. 1, p. 190.) When, however, the oospore does not fill the oogonium, its 

 germ-tube may meander about to quite a considerable extent in the space 



' It is, of course, well known that, in some groups of the higher plants, cellulose is found deposited 

 as a reserve material in thickened cell-walls ; but, so far as 1 am aware, it has not previously been 

 found stored in this manner amongst the fungi. The dissolution of this wall in the manner 

 described was followed in all cases where the stages of germination of oospores were actually kept 

 under observation from start to finish. One case was found, however, in an old culture where an 

 oospore had already produced a germ-tube of considerable size, while the somewhat thin oospore 

 wall, although haying an irregularly waved inner margin, was not reduced in thickness so completely 

 as to leave only its outer resistant larger. It would therefore appear that the total solution of the 

 inner cellulose wall of the oospore need not necessarily precede the development of the germ-tube. 



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