150 INTERNATIONAL CONGRESS OF VITICULTURE 



Plate II. 

 Haustoria and mycelium of Plasmopara viticola. 



Fig. 1. A haustorium which is still enclosed in the sheath of host cell- 

 wall, x 650. 



Figs. 2-5. Showing the goblet-shaped sheath about the base of the 

 haustoria. In figures 2, 4 and 5 the plasma membrane is pressed 

 inward but not penetrated, x 750. 



Fig. 6. The formation of the mycelial cushion beneath the stomate, 

 previous to conidiophore formation, x 750. 



Fig. 7. The mycelium bursting through the epidermis of the petiole to form 

 conidiophores. x 750. 



Plate III. 

 Fructifications of Plasmopara viticola. 



Figs. 1 and 3 show the effects of cuprammonia on the basal portion of the 

 conidiophore. x 300. 



Fig. 2. The basal portion of a normal conidiophore. x 300. 



Fig. 4. Showing the comparatively slight effect of cuprammonia on the 

 distal end of the conidiophore. x 300. 



Fig. 5. A conidium attached to the sterigma showing the lenticular dis- 

 junctive region, x 750. 



Figs. 6 and 7. The zoospores. In figure 7 two of the zoospores are attached 

 by a slender strand of protoplasm. Figure 6 x 750. Figure 7 x 375. 



Figs. 8-10. The germination of the conidia by zoospores. 



Fig. 11. Conidia produced by the germination of the zoospore. 



Plate IV. 



A few stages in the development of the oospore. 

 Fig. 1. A multinucleate oogonium. The nuclei are apparently zonate. 



Probably following a division since there are disintegrating nuclei 



occurring abundantly, x 750. 

 Fig. 2. An oogonium and antheridium. x 300. 

 Fig. 3. An oospore containing a single nucleus lying near a dark body 



which may be interpreted as the coenocentrum. Lying outside of the 



thick wall are remains of extraneous nuclei, x 750. 

 Fig. 4. A single nucleated oospore which contains a coenocentrum and 



what appear to be remnants of other nuclei lying near. About the 



margin are other dark bodies, probably the remains of nuclei which 



migrated from the centrosphere. x 750. 

 Fig. 5. An immature oospore about which the endosporium is being 



formed. There is an abundant periplasm present, x 750. 

 Fig. 6. A practically mature oospore, x 750. 



Plate V. 



Sections of healthy and diseased shoots. 



Fig. 1. A cross-section of a healthy petiole of a leaf, x 300. 



Fig. 2. A cross-section of the diseased petiole of approximately the same 



age as that shown in figure 1. This section also was taken from the 



same position on the petiole. The intussusception of the mycelium 



very largely explains the hypertrophy of the diseased petiole, x 300. 



