The morphology and growth of the vegetative and reproductive apices of Arabidopsis thaliana (L.) Heynh., Capsella bursa-pastoris (L.) Medic. and Anagallis arvensis L.

The structure and growth of the vegetative, inflorescence and floral apices of Arabidopsis thaliana (L.) Heynh., Gapsella bursa-pastoris (L.) Medic, and Anagallis arvensis L. have been investigated. The vegetative apices of all three plants show tunica and corpus zones and the normal cyto-histological zonation. Leaf primordia are initiated by periclinal divisions in the second tunica layer of the apex, and show apical and marginal growth during their early development. Leaf procambium development is always continuously acropetal. In Anagallis, axillary vegetative buds arise as detached parts of the apical meristem and their traces develop basipetally to join the traces of the sub. tending leaves. No marked morphological changes are to be observed in Anagallis during the formation of the inflorescence, but, in Arabidopsis and Capsella, marked changes have been observed and have been fully described. The inflorescence apices of all three species show tunica and corpus zones and a cyto-histological zonation. It has been shown that these apices are essentially similar to those of vegetative shoots. Flower primordia are initiated by periclinal divisions in the third layer of the flank meristem of the inflorescence apex. Procambium development to the flower primordia is continuously acropetal. The floral apex shows tunica and corpus zones. All the floral parts are initiated by periclinal divisions in the second tunica layer, and procambium development to these parts is again continuously acropetal. A possible homology between foliage leaves and flower parts has been discussed. 13. In all three plants, the petals are the last of the flower parts to mature.