On the grain-field weeds of the American Farm School of Thessaloniki
Acccording to Braun-Blanquet's system, the weeds of the American Farm School can be classified into two associations. One is characterized by the dominant species: Solanum elaeagnifolium and Hypericum perforatum, and the other by the dominant species: Sinapis arvensis and Leontice leontopetalum. Both these can be considered as new for Europe. Of the two associations, the first one consists of the characteristic species: Solanum elaeagnifolium, Hypericum perforatum, Vicia eriocarpa, Cynodon dactylon, and Chenopodium opulifolium. Most of them are sun loving plants and grow most abundantly in dry soil and in places where crops are sparsely grown. The plants that grow on the area covered by this community are mostly therophytes. There are few hemicryptophytes and geophytes. All the plants cover 45 to 75 per cent of the total area, while the weeds cover 6 to 10 per cent. The average number of species of an area of 10 x 10 m is between 30 to 40. The second association consists of the characteristic species: Sinapis arvensis, Leontice leontopetalum, Fumaria officinalis, Melilotus segetalis, and Vicia tenuifolia fo. platyphyllos. The most abundant and most frequent among these are Sinapis arvensis and Leontice leontopetalum. The most troublesome to cultivation is Sinapis arvensis. 74 per cent of the total number of species of this association are therophytes. Annual or biennial hemicryptophytes, as well as rhizomatous or bulbous geophytes are few or very few. This association extends especially on sandy loam soils, where the moisture is higher than in the soils where the Solanum elaeagnifolium-Hypericum perforatum ass. extends. The cover of vegetation there is 60 to 80 per cent, while the cover of weeds 10 to 20 per cent. The number of species found in an area of 10 x 10 m is about the same as in the previously mentioned association. Most of the plants that grow on the edges of the fields are annual or more frequently biennial hemicryptophytes. Of the climatic conditions, the spring distribution of rainfall, as well as the air temperature seem to be the most important factors which influence the foliage, flowering, fruiting, and shoot and rootstock development. The methods of control do not seem to have much influence upon the composition or the number and plenteousness of the plant communities.