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The leaves of many tropical trees have besides the normal stomata abnormally large stomata long described as "giant stomata." They reflect an additional early phase of stomata initiation during leaf ontogeny. In epidermal replicas from more than 200 dicotyledonous species of temperate climate we also found well defined giant stomata or solitary stomata of normal size in the majority of woody plants, but rarely in herbaceous plants. There is no relationship between taxonomic group and presence of giant stomata.

root growth of two pioneering plant species on soil development during the initial stage of ecosystem genesis in the Lusatian post mining landscape. Can. J. Soil Sci. 92: 67Á76. To characterize the role of root growth of Lotus corniculatus L. (bird's-foot trefoil) and Calamagrostis epigeios L. Roth (chee reed grass) in soil development during the initial stage of ecosystem genesis, the root systems of these plant species growing in soils from quaternary calcareous sediments were studied. The spatial distribution pattern of root systems varied considerably. Both plant species contributed to the accumulation of organic carbon in the bulk soil, although the highest concentrations were from the legume L. corniculatus. Total nitrogen concentration in the bulk soil was not affected, but increased in the rhizosphere soil of both plant species. There were clear indications that both plant species contributed to homogenizing phosphorus distribution, resulting in phosphorus depletion of those soil compartments where root proliferation was highest. Pronounced differences were detected between plant species, which led to the conclusion that the homogenizing effect caused by one species on a plot level may be overridden by the heterogeneity of patches composed of different plant species at the ecosystem level. All considered components suggest that the development of root systems of herbaceous pioneer plant species provides significant contributions to land reclamation in a natural way.Boldt, K., Schneider, B. U., Fritsch, S. et Hu¨ttl, R. F. 2012. Impact de la croissance des racines de deux plantes pionnie`res sur le de´veloppement du sol pendant l'e´tape initiale de gene`se d'un e´cosyste`me apre`s exploitation minie`re, en Lusace. Can. J. Soil Sci. 92: 67Á76. Les auteurs ont e´tudie´le syste`me racinaire du lotier cornicule´(Lotus corniculatus L.) et de la calamagrostide commune (Calamagrostis epigeios L. Roth) poussant sur un sol contenant des se´diments calcaires du Quaternaire en vue de pre´ciser le roˆle des racines dans le de´veloppement du sol lors de l'e´tape initiale de la gene`se d'un e´cosyste`me. La re´partition des racines varie conside´rablement dans l'espace. Les deux espe`ces concourent a`l'accumulation du carbone organique dans le sol brut, mais c'est au lotier, une le´gumineuse, qu'on doit la plus forte concentration. La concentration d'azote total dans le sol brut n'est pas affecte´e, cependant elle augmente dans le sol de la rhizosphe`re des deux plantes. Tout indique que les deux espe`ces contribuent a`rendre la re´partition du phosphore homoge`ne, ce qui entraıˆne l'e´puisement de cet e´le´ment dans les parties du sol ou`leurs racines prolife`rent le plus. Les auteurs ont de´cele´des variations prononce´es entre les deux espe`ces, ce qui les incite a`conclure que l'homoge´ne´isation cause´e par une espe`ce dans une parcelle peut eˆtre compense´e, au niveau de l'e´cosyste`me, par l'he´te´roge´ne´ite´observe´e aux endroits ou`poussent diverses espe`ces. Tous les e´le´ments examine´s laissent croire que l...