Vegetative propagation in bryophytes is achieved by isolation of new centers of subapical growth (“branches) at the protonematic level as well as at the foliar axis level. There are also specialized vegetative areas which secure, like the thallospores and the conidiocysts of Thallophytes, an immediate or delayed propagation of these plants. The role of light has been studied on growth and ramification (of the protonema and of the foliar axis) as well as on reactivation of initials. Photomorphogenesis is regulated at least by three photoreceptors systems: the system of chlorophyll pigments, the phytochrome system, a photoreceptor system in blue light, antagonist to the phytochrome. Researches are discussed according to the responses obtained from the modification of the three components of the light factor, that is to say light intensity, light rhythm and light wavelength.
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