Pethybridgk and Murphy— 0?« Phytophthora infestans. 587 



EXPLANATION OF PLATES. 



All dra-wings were made with the help of a camera lueida under a Leitz micro- 

 scope with objective 9 and ocular 2, giving a magnification of approximately 

 730 diameters, and are reproduced reduced to about two-thirds of the original 

 size, viz. 486 diameters. Our thanks are due to Mr. H. A. Lafferty for the 

 drawings (made under our supervision) of figs. 1, 2, 3, 11, and 12. The contents 

 of the spores in figs. 7, 8, 9, and 10 are necessarily somewhat diagramatically 

 represented. The reproductions of photographs in Plate XLV are from the 

 original, untouched negatives. 



PLATE XLV. 



Fig. 1. Pure culture of P. infestans on Quaker-Oat agar (to which some lamp- 

 black was added previous to steriHzation in order to increase the contrast 

 between the fungus and the medium), showing eight days' growth at 

 room-temperature. Conidia were abundant. (Reduced.) 



Fig. 2. Pure cultures of P. infestans on Oat agar slants in test-tubes. (Eeduced.) 



Fig. 3. Oogonia as seen embedded in the Quaker-Oat agar medium under low 

 power of microscope (Leitz Objective 3, Ocular 2). 



Fig. 4. A young spherical oogonium (with oosphere faintly visible) grown on 

 Clinton's Oat-juice agar, x 625. 



Fig. 5. A spherical oogonium (touching a hair from the Oat), after gentle 

 pressure on the cover-glass has caused it to burst, showing the 

 parthenogenetically formed oospore within. Grown on Clinton's 

 Oat-juice agar, x 375. 



Fig. 6. A pyriform oogonium burst open, with the liberated oospore. Grown 

 on Clinton's Oat-juice agar, x 375. 



Fig. 7. Oogonium and antheridium of P. infestans grown on Quaker Oat Agar. 

 The oogoniumcontains a ripe oospore which nearly fills it ; and the less 

 dense central portion of its contents is faintly discernible. The funnel- 

 shaped base of the oogonium within the antheridium is clearly visible ; 

 but the hyphae bearing the antheridium and oogonium are not present 

 in this instance, having been broken away, in all probability, during the 

 preparation of the specimen, x 730. 



PLATE XLVI. 



Figs. 1, 2, 3. Abnormalities or deformities seen in mycelium growing submerged 

 in potato-juice sterilized by filtration through a Berkefeld candle. They 

 are probably to be regarded as abortive conidial growths. 



