It was shown that plants of different types of development (winter-annual, alternate, spring-annual) with vegetation periods of different lengths differ in their reaction to light at the vegetative phase, requiring different amounts of light energy for transition of the sprout growth cones to formation of rudimentary efflorescences (stage IV of organogenesis). The more light that is required, the longer the time needed to satisfy the light requirement, the longer the period of vegetative development (phase of tillering) and, finally, the longer the vegetation period and the more strongly expressed the plant's winter-annual pattern. As a result of vernalization, plants of all types, almost equal in their reaction to light and length of vegetation period, approaching spring-annual plants, thus providing for normal development and timely maturation during the favorable spring-summer season. © 1999 MAEe Cyrillic signK "Hayκa/Interperiodica".