Onset of Reproductive Phase in Grasses and Cereals

Abstract

IN the Gramineae inflorescence production commences suddenly: the new primordia arising at the apex remain small but their axillary buds appear precociously and rapidly begin to develop into spikelets or groups of spikelets, according to the species. The abruptness with which vegetative growth changes over to inflorescence production suggests that there is a sort of minimum condition in the internal economy of the shoot apex which must be reached, and that once the point of balance is passed the vegetative type of growth ceases. The obvious suggestion is that the onset of the reproductive phase only occurs when a certain carbohydrate/nitrogen (C/N) ratio is reached. If this is the case, it should be possible to alter markedly the number of leaves produced before inflorescence production by altering the nutriment in which the plants are growing. Purvis1, however, has shown that the amount of nitrogen supplied to rye seedlings has little effect. Plants grown under long days (16 hours) and manured with a full culture solution and 1/10 N culture solution produced 13.3 and 12.4 leaves respectively if germinated at 1° C. and 21 and 20.59 leaves respectively if germinated at 18° C.