Kaszab Zoltán (szerk.): A Magyar Természettudományi Múzeum évkönyve 64. (Budapest 1972)

Szujkó-Lacza, J. ; Fekete, G.: A survey of the plant life-form systems and the respective research approaches IV. Taxonomic aspects of the life-form protection of the embryonal and meristematic tissues in the dormancy stage

cept. In artificial shoot-producing experiments it was found that the bud scales render mechanical protection to the embryonal tissues by creating anaerobic conditions: a certain amount of C0

2 accumulates, and changes in a number «?£ biochemical substances coidd also be demonstrated in the dormant buds (SAMISH, 1954). The rest period or the dormancy of plants is a temporal phase in the life cycle of every plant, irrespectively whether the rest period sets in during the vegetative or generative (seed) form. Dormancy is the retardation of seed germination or bud growth even if conditions are otherwise suitable for growth and development. According to SAMISH (1954) : "Dormancy is generally associated with the suppression of visible growth, especially that of buds and seeds, without regard to its cause". CROCKER (1948) attempted to summarize the conditions, and to describe their mechanisms, under which the germination of seeds are retarded. They are: "a. rudimentary embryos that must mature before germination can begin, such as found with holly and orchid; b. seeds showing complete inhibition of water absorption, such as legumes and water lotus; c. mechanical resistance to the expansion of the embryo and seed contents by enclosing structures; d. encasing structures interfering with oxygen absorption by the embryo and perhaps carbon dioxid elimination, resulting in the limitation of the processes dependent upon these, as observed with seeds ; e. a state of dormancy in the embryo itself or some organ of it, in consequence of which it is unable to grow with full vigor but may show sluggihs development when naked and supplied with all ordinary germinative conditions ..." Literature is extensive on the anatomical structure, the mechanical and in a certain sense physiological role of the bud scale and the seed coats. We deemed it sufficient to cite solely this fundamental statement for a knowledge of the role played by the characteristic organs of the plant life-forms, or the essence of dormancy. Concerning the function of dormancy, we may accept THORNTON'S (1953) summary remark: "Nature of the protoplasm, seed coats, and light effects are. . . nature's means of insuring an extension in life span of the organs of reproduction of plants." In our own words, dormancy is the rest period of the meristematic and embryonal tissues protected by bud scales or seed coats, delimited by the exterior environmental conditions and the internal cytological state, as a residt of which the physiological processes become inhibited in these organs. As far as the origin of dormancy is concerned, MEYER et ANDERSON (cited by SAMISH, I.e.) point out the external environmental conditions, and more nearly the unfavourable temperature, water supply etc., as the causative effects. CHANDLER (in SAMISH, I.e.) designated dormancy induced by the unfavourable external conditions by the term quiescence, thereby separating it from the concept of rest, originating, according to him, from inner factors. For corroboration, CHANDLER introduces examples in which growth ceases although the external conditions are favourable. Extending this train of thought, SAMISH remarks that "The entrance into rest is usually preceded by a stage of quiescence either brought about by shorter days, cold, heat, drought, or other conditions unfavourable to growth, or due to correlative inhibition..." ..'."It is important to distinguish between stages of rest and quiescence in reporting experiments of dormancy". NITSCH demonstrated experimentally that it is the foliage leaves which transport substances inhibiting bud growth under short-day conditions. His experiments fail to justify convincingly — especially in the causative sense — the definite separation of quiescence and the