Dorothy M. Cayley 477 



DESCRIPTION OF PLATES. 



PLATE IV. 



Fig. 1. Peas germinated in a cool greenhouse in soil partially sterilized by heat. 

 1, 1, 2, 2. Diseased seed. 

 5. Control, healthy seed. 



Fig. 2. A. Healthy plant, just before flowering period. 

 B. Four diseased plants of the same age. 



PLATE V. 



Fig. L A. Seven diseased seeds germinated in sterile sand in a petri dish. 

 B. Typical healthy seedling grown in a pot. 



Fig. 2. Pea seed enlarged, two years old, kept in sterile sand to germinate. No germina- 

 tion. The contoured growth (a) on the testa is a pure growth of Ps. seminum. 

 (b) Grains of sand still adhering. 



Fig. 3. Giant colonies of Ps, seminum enlarged, growing on neutral pea agar agar. 



(a) Submerged colony. 



(b) Surface colony. 



Fig. 4. Same culture as in Fig. 3, but growing on alkaline pea agar agar. 



(a) Submerged colonies. 



(b) Surface colony. 



Fig. 5. Platings of Ps. seminum. 



(a) Acid (I per cent, normal HCl) pea agar agar. 



(6) Alkaline (1 per cent, normal NaOH) pea agar agar. 



(c) Neutral pea agar agar. 



PLATE VI. 



Fig. 1. Microtome section of epidermal cells of young embryo of pea germinated in 

 sterile sand, showing penetration of bacteria into uninjured cells and into the inter- 

 cellular spaces. 



S.W. Swollen cell wall. 



I. Intercellular space, filled with bacteria, stained Carbol Fuchsin and Licht Griin. 



Fig. 2. Microtome section of phloem parenchyma of young diseased stem infected with 

 Ps. seminum. 



S.W. Swollen disorganised cell wall. 



B. Bacteria. 



H. Healthy cell wall. 



Fig. 3. Microtome section of cotyledon of pea germinated in sterile sand. 

 B. Bacteria. 



D. Disorganised cell walls. 

 H. Healthy cell wall. 



I. Intercellular spaces filled with bacteria. 

 S. Starch grains. 



