The elongation of light grown gherkin seedlings in blue light can also be obtained in red light in the presence of auxins. The elongating effect of blue light on light grown seedlings can be antagonized by anti-auxins. Light grown seedlings transferred to darkness show a toxic effect after a pretreatment with blue or infra-red radiation. The same effect can be obtained by a pretreatment with red light when auxins were added. Plants pretreated with red light without an application of auxins do not show this typical effect.