Narcissus and Daffodil

The biology of Narcissus 7
Figure 1.5 Centre: double-nosed bulb, narcissus ‘Carlton’. Right: separation of offsets.
Left: offset (top) and large ‘mother bulb’ (below). (Photograph: Horticulture
Research International.)
As narcissus bulbs are branching systems, lateral bulb units are initiated as well
as the terminal, replacement units. The presence of lateral as well as terminal bulb
units, and the gradual separation from the cluster of bulb units derived from laterals
(‘offsets’), results in a variety of bulb shapes and sizes, from round single-nosed
bulbs to double- and multi-nosed bulbs (the latter also termed ‘mother bulbs’),
together with smaller attached or detached, usually non-flowering, offsets (Figure 1.5).
The life-span of individual branching systems is not known for narcissus cultivars,
although Barkham (1980a) recorded half-lives of adult N. pseudonarcissus of 12–18
years, and Koopowitz (1986) suggested that, judging from other Amaryllids, they
are likely to have a high longevity.
Terminal bulb units are initiated alongside the flower initial of the previous bulb
unit, in the axil of the second leaf from its centre, at or shortly after floral initiation
in May (Rees, 1969). Lateral bulb units are initiated, usually in the axil of the third
leaf from the centre, in the following December. Supernumerary (lateral) bulb
units may also be initiated in the same year as regular laterals or a year later, in the
axil of a bulb scale (usually the innermost scale) or alongside the regular lateral.
The classification of bulb units was elegantly described by Rees (1969) (Figure 1.6,
Table 1.1). Each terminal bulb unit is replaced by two ‘daughter’ units, terminal
and lateral, while lateral units rarely contain a lateral unit. This gives a slow increase
in bulb unit numbers, increasing in a Fibonacci series 1, 1, 2, 3, 5, 8, 13..., an
increase tending to 1.6-fold per annum, producing a population made up of 38%
lateral units. In commercial bulb growing, this progression is prevented by the
grading-out of saleable bulbs, and, possibly, by the suppression of laterals under
sub-optimal conditions. In the earlier study by Okada and Miwa (1958) on a