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

in question into extreme conditions (cultures). There is no essential difference between the two methods. According to SEREBRIAKOV, there evolved from those types in which the orthotropic shoot growth was superseded hy the growth form having the plagiotropic shoots as the most intensely developing ones, the life-form of the procumbent nanophytes, prostrate shrubs, and pulvinately growing nanophytes, mainly in the high mountains and the arctic zone. A special form of nanic stature evolved in regions with an arid, continental and cold winters. By the recurrent demolition of the greater part of the annual orthotropic shoot, the suffrutescent life-form evolved in a number of families (Chenopodiaceae, Gompositae, Caryopliyllaceae, Polygonaceae, etc.). This life-form is rarer in arctic regions. The development of the mighty primary root ran parallel with these modifications. The safest survival for the renovating buds is secured by a position slightly above the soil surface. According to observations, these types brought into being the tap-rooted forms of the Hemicryptophyton life-form. A Hemicryptophyton life-form and a gramineous stature evolve, however, along also other fronts, e.g. in the arctic line from the pulvinate suffrutescents. The genus Salix permits several possibilities to study life-form evolution within a given taxon. The descent and development of the taxa of this extensive genus containing 491 species ran, according to their monographers BUSER (1940) and SCHARFETTER (1953), in many respects parallel with the evolvement of their stature and life-form. The system of the genus is based on the morphology of the generative organs (number of nectaries and stamens, development of the catkin, etc.). The oldest group (Salices Pleiandrae) reveals a relationship with the genus Popul us; species living in Europe. North America, and Asia belong here — the centre of their range extending from Asia Minor to India. Many species are ramifying monopodially and arborescent. Although deciduous, there are also tropical species with persisting leaves, shedding them only by the appearance of the new shoot. Their ancestral rank is substantiated by the Tertiary fossil finds belonging also exclusively to the Pleiandrae group. The mighty, arborescent Salix species appeared in considerable numbers, in their Mega- and Mesophanerophyton life-forms, during the Cretaceous (cf. HANSEN. L956). Tropical mountainous ranges are indicated by the authors as the place of origin of a more derived Salix group. The ancestors of the Salices Diandrae may have been Oreophytons according to these workers; these forms are characterizable by the sympodeal ramification parallel with the reduction of the stamens and nectaria. This kind of ramification made possible in the Salix forms the reduction of the vegetative organ, the development of the Chamaephyton life-form, of the nanic and prostrate shrub growth forms. By these same authors, the reductions had probably came into being during the early glaciations, representing phylogenetical steps as well. We are dealing with arctic and alpine species; the best known ones are Salix reticulata, herbacea, refusa, ser pyllifolia, etc. By the paleobotanical evidence, the ancestors, with a Nanophanerophyton and Chamaephyton life-form, of the species enumerated above, partly recent forms, can be found abundantly in the Quarternary. The S(dices Mononectariae resulted from a further simplification of the flower structure and the subsequent reduction of the nectaria. That the members of this group are the youngest ones is proven also by the fact that there is none among them common to the Eurasian and North American continents: the origin of the group must have happened later than the separation of the continents. This new