The California Vine Disease; A Preliminary Report of Investigations (Paperback)

Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: CHAPTER III. SPECIAL CHARACTERS OF THE DISEASE. THE LEAF. As in the healthy vine, the size of the leaf varies according to its position upon the cane, is usually in direct proportion to the size of the latter, and is dependent upon its vigor of growth. As might naturally be inferred, vines in the second or later years of disease, when there is less vigor and consequently a shorter growth of cane, produce leaves smaller than those borne by healthy or recently diseased vines. On the other hand, there is very rarely, if ever, any such disproportionate reduction in the size of the leaf under the influence of this disease as is seen in the case of vines grown in cold or alkaline soils or affected by root fungi. In fact, the proportions of the leaf to the cane and top of the vine are, in general, so well maintained, that the reduction in the size of the leaf does not impress one except in later stages of the disease or by direct comparison. The petiole retains its proper proportions. In a majority of the diseased vines, although not in all varieties, the leaf presents distinct characters. They may be mentioned as constitutional and localized characters. The localized characters are those of the leaf affected after it has become fully and perfectly formed, but only including the local effects of the disease. The constitutional characters are those of a leaf never becoming perfectshowing a diseased state from the time of its openingor those of a matured leaf subsequently affected in a constitutional way. The constitutional effects upon the leaf become apparent in two ways: (1) The chlorophyll of the newly formed leaf fails to properly develop in that portion of the parenchyma lying slightly distant from the main flbro-vascular bundles, or in that part supplied only by ...