Initiation of Procambial Strands in Leaf Primordia of Dactylis glomerata L. as an Example of a Temperate Herbage Grass

This study is concerned with the examination of shoots of herbagegrasses, particularly Dactylis glomerata L., for comparisonwith earlier investigations on this species and on the cerealTriticum aestivum L. The main features of procambial strandinitiation are found to be the same in all the herbage grassesexamined and to be very similar to those in Triticum. Thus,in a vegetative shoot, all the procambial strands originatein the leaf primordia independently of the vascular system ofthe older parts of the plant, and extend downwards from theirfirst point of origin. For the median strands, the first pointof origin is in the disc of insertion of the primordium, butfor later strands it is progressively higher, so that the laststrands 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, isvery regular and predictable. However, two discs of insertionbelow the point of initiation of strands, their course is interruptedby the strands of the primordium directly below (there is onealternating primordium between them), and from this point downwardsvariations, both specific and between individual plants andprimordia, occur. This is the region where connexion with thevascular supply of the rest of the plant is first established.The timing of the arrival of young strands from above and ofthe development of successive nodal plexi from below, via whichmost interconnexions are established, will give some variationto the early development of this region.