The physiology of flowering in Pisum sativum (the garden pea)

Late varieties of the garden pea are quantitatively long day photo-periodically sensitive and can be vernalised (Barberm, 1959). This was verified and the increased response to day length and vernalisation in the tall late variety Telephone over the dwarf late variety Greenfeast was noted. Late varieties of garden pea grown in the field flowered at a lower average node than was found with any of the plants grown in growth environmental chambers and attempts were made to simulate under controlled conditions the variations between plants grown in the field and plants grown in growth cabinets. Lowering the intensity of light incident on plants reduces plant height and dry weight but does not affect flowering. High intensity blue light and various ratios of red to far red supplementary light were tested but these did not affect plant growth or flowering. Different growth media (soil, peralite with nutrient solution) and the presence or absence of root nodules were tested and found to have no effect on growth or flowering. The effect of gibberellic acid on growth and flowering were studied and it was shown that a natural dwarf late variety given the phenotype of a tall variety by applications of gibberellic acid would respond to day-length and vernalisation in a similar manner to a natural tall late variety. A general delay in flowering and fruit set in both natural tall and natural dwarf varieties was noted after applications of gibberellic acid and this was noted to be more pronounced under short day growth conditions. The effects of the removal of cotyledons on growth, development and flowering of garden pea plants was studied and it was shown that after removal of the cotyledons plant growth rate was reduced, internodes were shorter, leaflets were smaller and plants flowered earlier than control plants which had retained their cotyledons. It was also shown that the reduced vegetative growth rate continued throughout the entire life of the plant provided that the cotyledons were removed before 240 hours after planting, and that plants without cotyledons flowered at a lower average node than controls provided that the cotyledons were removed within 120 hours of planting. Various compounds (gibberellic acid, sucrose, kinetin, indolyl acetic acid and pea cotyledon extracts) were applied to decotylised plants in attempts to restore vegetative vigour and normal flowering pattern. All compounds failed completely to restore the vegetative vigour and normal flowering pattern of the controls. Parts of the cotyledon complement were removed and the effects on growth and flowering were recorded. One quarter of the cotyledon complement was shown to be adequate to allow plants to flower normally and one complete cotyledon was sufficient to allow for normal growth. It was shown that decotylised plants could be vernalised and that the cotyledons are not the site of perception of the cold stimulus of a period of vernalisation