Wasting Disease of Zostera marina

Abstract

IN Dr. Kathleen B. Blackburn's letter on this subject¹, the conclusion seems well established, through a study of the chromosomes, that the narrow-leaved form of the eelgrass (grass wrack), which has in many of the diseased areas replaced the larger and broader type of plant, is clearly a form of Z. marina and not a hybrid of Z. marina and Z. nana, as some have believed. Miss Blackburn therefore suggests that the difference in the width of the leaves of varieties of Z. marina may be a purely ecological character. She further remarks that, in the localities examined, the width of the leaf of Z. marina was directly proportional to the depth of the water, and that the very narrow-leaved forms Were those that had been longest exposed by the fall of the tide, while the broader were those that had not been exposed at all.