The Leaf-Base and the Interdone- Their true Morphology

Abstract

1. Development of the leaf primordium at the shoot apices of 14 species of dicotyledons has been studied. 2. These include exstipulate, stipulate and sheathing leaves with or without a free base. 3. The axial component which is laid down first during the initiation of a leaf development at the apex of a vegetative shoot is a part of the leaf and is to be considered as its base. 4. In species where a free base is wanting, the axial component represents the only base and the cauline and discontinuous stipular scar, which led Ponzo, Cross and others to doubt the origin of stipules from the leaf-base, is explained. 5. The development of a free base in the form of a sheath and/or a pair of stipules depends on the course and behaviour of the trace bundles through the axial component (e.g. in species of Centella, Polygonum, Ixora, Ervatamia, Rosa, Morus, Calotropis, Artocarpus, Ficus, Paederia, Hibiscus and Pisum). 6. If the laterals change their vertical course, bend and follow an oblique horizontal course towards the median at the top of the axial component, the petiole appears to be inserted directly on the axis without any evident base (free) as in the species of Ficus, Paederia, Jasminum, Hibiscus, Morus and Pisum studied. 7. If during the horizontal course the laterals branch in the axial component, a single (Ficus elastica, Ervatamia divaricata, Polygonum orientale), or a pair of stipules (Ficus religiosa, Artocarpus integrifolia, Morus alba, Hibiscus rosa-sinensis, Pisum sativum and Rosa centifolia ), or a composite stipule (Ixora parviflora and Paederia foetida), are formed with the branches as their traces, and the stipular scars appear cauline. 8. If the laterals, two or many, run almost parallel to one another and to the median, even after leaving the axial component for some time before they turn towards the median, a sheathing but free base is formed which partially or completely encloses the axis, depending on the number and nature of the course of the laterals (e.g. Centella and Rosa). 9. If in a multilacunar node the laterals branch during their horizontal course towards the median the stipule formed is either an ochrea (Polygonum), or bud scales (species of Ficus and Artocarpus). 10. If, however, the laterals do not branch and gradually shift towards the median where they form with the latter a ring of vascular bundles, the sheath becomes oblique and tapering without any stipule (Centella). 11. The base, i.e. the axial component, and its free portion, if there be any, can be anatomically distinguished by the nature and behaviour of the laterals, from the petiole: in the base they gradually approach the median without joining it and may branch, but in petiole they either join with the median (Rosa) or arrange themselves with the latter in the form of a ring of vascular bundles (Centella). They again branch in connection with leaflet and lamina formation. 12. The internode is made up of an axial core and a mantle derived from two different zones of the eumeristem - the corpus and the flank meristems. The mantle is made by base or bases (axial component or components) of the leaves, and extends radially up to the pith as suggested by Hofmeister.