THE MODE OF PENETRATION OF PEAR AND APPLE BLOSSOMS BY THE FIRE-BLIGHT PATHOGEN

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Abstract
Histological studies of pear and apple blossoms reveal a well-defined cuticle in the nec-tarial regions. The nectar, instead of exuding from naked cells, as usually assumed, passes out through stoma-like openings, which are regulated by guard cells. For these nectar-exuding structures the term "nectarthodes" is proposed. The fire-blight pathogen gains entrance into the nectarial tissues by means of these nectarthodes; such entrance is less frequent in apples than in pears. The reason for this difference is seen in the narrow, elongated, tightly covered calyx cup, characteristic of apple blossoms during nectar flow, contrasted with the broad, open, and shallow calyx cup characteristic of pear blossoms. In addition to penetration through nectarthodes, Erwinia amylovora penetrates the following floral parts of pears and apples: stigmatic surfaces, and anther locules.

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