Lime Plants Research Articles

Yellow-vein disease of citrus and studies of interactions between yellow-vein and other viruses of citrus

A virus that produces marked vein yellowing was found in four Eustis limequat trees in California. It had a wide host range within the citrus family but did not persist in some varieties. Poncirus trifoliata was immune from the yellow-vein virus. There was no evidence of natural spread of the virus in the field. The virus was transmitted by several methods of tissue grafting. It was not transmitted by Cuscuta subinclusa or by mechanical means. Protection against infection by the yellow-vein virus was not provided by the viruses of cachexia, exocortis, psorosis, tristeza, and vein enation. When lime plants were inoculated with the viruses of yellow-vein and psorosis, yellow-vein symptoms in new growth were always suppressed and psorosis symptoms enhanced as compared to those in single virus infections. The dominance of psorosis in new growth resulted regardless of the sequence of introduction of the virus components of the mixture. When yellow-vein was established prior to infection with psorosis, yellow-vein symptoms already showing were not affected, but in subsequent growth, yellow-vein was suppressed. Several citrus varieties, including lemon, Florida Rough lemon, and sweet orange, inoculated with yellow-vein developed mild vein-yellowing symptoms but soon recovered as the plants continued to grow. When these recovered plants were inoculated with vein-enation virus, severe yellow-vein symptoms reappeared and severe dwarfing resulted. The synergistic reaction developed regardless of the order of inoculations. Vein enations were discolored and apparently enlarged in the presence of the yellow-vein virus.

On the function of silica in the nutrition of cereals.―Part I

The presence of silica in plants was first demonstrated by the analyses of De Saussure, who pointed out that the Gramineæ were particularly distinguished by the large proportion of this constituent present in their ash. Liebig, who classified plants as “silica plants,” “lime plants,” and “potash plants” according to the predominance of one or other of these constituents in their ash, in accordance with his “mineral theory,” regarded the silica as a necessary element in plant nutrition. This view led Way to introduce as a cereal manure a rocky material derived from the Upper Greensand near Farnham, which contained a considerable proportion of silicate easily soluble in acids. But when Sachs succeeded in maturing maize plants in water cultures containing no silica, whereby the proportion of silica in the ash of the mature plant was reduced from the normal 20 per cent. or so to as little as 0·7 per cent., it became evident that silica could no longer be placed in the same category as phosphoric acid and potash as essential elements of plant nutrition, and Jodin raised four successive generations of maize in water cultures without any supply of silica beyond that contained in the original seed. Other investigators again showed that the stiffness of cereal straw, which had been attributed to the presence of silica, depends on the development of the internodes under the influence of such factors as illumination and exposure.