This study is concerned with the examination of shoots of herbage grasses, particularly Dactylis glomerata L., for comparison with earlier investigations on this species and on the cereal Triticum aestivum L. The main features of procambial strand initiation are found to be the same in all the herbage grasses examined and to be very similar to those in Triticum. Thus, in a vegetative shoot, all the procambial strands originate in the leaf primordia independently of the vascular system of the older parts of the plant, and extend downwards from their first point of origin. For the median strands, the first point of origin is in the disc of insertion of the primordium, but for later strands it is progressively higher, so that the last strands are initiated well up in the free portion of the primordium. The course of the median and first and second lateral strands, in the first two discs of insertion that they penetrate, is very regular and predictable. However, two discs of insertion below the point of initiation of strands, their course is interrupted by the strands of the primordium directly below (there is one alternating primordium between them), and from this point downwards variations, both specific and between individual plants and primordia, occur. This is the region where connexion with the vascular supply of the rest of the plant is first established. The timing of the arrival of young strands from above and of the development of successive nodal plexi from below, via which most interconnexions are established, will give some variation to the early development of this region. © 1968 OXFORD UNIVERSITY PRESS.
