198 Scientific Proceedings, Royal Dublin Society. 



EXPLANATION OP PLATE XIII. 



The reproductions of the photo-micrographs in this plate are from the original 

 untouched negatives. 



Fig. 1. Eipened sexual organs of Phytophthora erythroseptica photographed from 

 living material. The oogonium, with its funnel-shaped base (containing 

 a cellulose plug) within the antheridium, contains in its spherical 

 portion an oospore with a thick wall, granular peripheral protoplasm in 

 which the oval body can be seen, and a central large oil-drop, x 500. 



Fig. 2. Ripened sexual organs after exposure to the vapour of osmic acid. The 

 central oil-drop is very deeply stained, the oval body less so, and the 

 granular protoplasm still less so. x 500, 



Fig. 3. Sexual organs viewed from above, showing an oospore in the early stages 

 of germination. Owing to the irregular manner in which the thick, 

 wall of the spore becomes dissolved, its inner margin is wavy. The two 

 short, thin, hypha-like structures in contact with the object are portions 

 of the medium, not of the fungus. Living material, x 900. 



Fig. 4. A conidium which, instead of producing either a germ-tube or a number 

 of zoospores, has burst at its apex, and the contents are oozing out. 

 x260. 



Fig. 5. A conidium (zoosporangium) fixed with iodine in potassium iodide 

 solution, showing the segregation of its contents into zoospore units. 

 The thicker, flatter, apical portion of the wall is clearly distinguishable ; 

 but the contraction of the contents away from the wall is somewhat 

 greater than is the case in living material, x 365. 



Fig. 6. A conidium germinating by the production of a single germ-tube. This 

 tube makes its exit a little to one side of the apex of the conidium, the 

 apical, thicker, more hyaline part of the conidial wall being seen to the 

 right near the base of the germ-tube. Living material, x 527. 



Fig. 7. Two conidia (zoosporangia), one of which has already discharged its 

 zoospores and become split during manipulation. The other shows 

 the segregation of the contents into zoospore units previous to their 

 emission, as seen from the basal end of the zoosporangium. Material 

 fixed in iodine in potassium iodide solution, x 370. 



Fig. 8. A group of four zoosporangia. The uppermost one on the left contains 

 undischarged zoospores; the one below it has emitted one zoospore, 

 which has come to rest and developed a germ-tube. In the centre is a 

 practically empty zoosporangium, while on the right is a partially 

 emptied one, two of the three emitted zoospores having produced 

 germ-tubes. Material fixed with osmic acid vapour, .x 354. 



