The bacteria is spread by insects or splashing rain, entering plants through tiny wounds. The bacteria begin to replicate, stimulating the surrounding plant tissues. The surrounding tissues begin to grow, eventually forming a large tumour, called a gall. Unlike other, more healthy plant parts, the tumour isn't protected by a surrounding layer of tissues (the epidermis). The lack of epidermis makes plants susceptible to secondary infections by other bacteria, fungi and insects. Secondary infections cause the gall to darken, turning-blackish brown. At this point, new bacteria are released in water or into the soil, where they can lay dormant until the following growing season, or even for years after.