Betula pendula scales. The foliage is a pale to medium green and turns yellow early in the autumn before the leaves fall. In mid-summer, the female catkins mature and the male catkins expand and release pollen, and wind pollination takes place. The small 1 to 2 mm winged seeds ripen in late summer on pendulous, cylindrical catkins long and broad. The seeds are very numerous and are separated by scales, and when ripe, the whole catkin disintegrates and the seeds are spread widely by the wind. Silver birch can easily be confused with the similar downy birch ("Betula pubescens"). Yet, downy birch
Citrus gummy bark viroid observed in longitudinal sections. Citrus gummy bark viroid The citrus gummy bark viroid (abbreviated CGBVd) is a sub-species of the hop stunt viroid, and thus is a member of the genus Hostuviroid. As the name suggests, the citrus gummy bark viroid causes problems in the bark of the sweet orange tree. Scrapping the bark exposes localized spots or a line of reddish-brown, gum-impregnated tissue around the scion circumference especially visible near the bud union. The discoloration and gumming may extend above the bud union to the main branches of the sweet orange while in severe infection dark streaks of gum-impregnated