90
N. WALOFF
The shrub is a much branched perennial and according to Mr D. F.
Fourt of the Forwtry Commission (pers. comm.) and to our own observations i t haa a lifo span of 10-15 years. The older bushes are especially
susceptible to stress caused by excessive flowering and ripening of
seeds, unusually severe winters and insect attack.
The green twigs are glabrous and 6-angled and the leaves, which are
small, appear in spring and may start falling as early aa the middle of
September. In early spring the bushes may form delicate leaves a t the
beginning of February, but these are usually killed by frost and new
foliage d.evelops a month or more later. The lower leaves are shortly
stalked and consist of 3 small obovate leaflets. The upper leaves are
single and sessile. Flowers may appear as early aa in the middle of March,
but full flowering usually takes place in May. However, its intensity and
time varies from year to year. The flowers are large, bright yellow and
occur singly or in pairs. These are borne on slender pedicels in the axles
of the old leaves, forming handsome leafy rtmmes along the upper
branches. When in flower, broom attracts a great variety of insects.
There are two main growth periods in the year, one in spring just
before flowering and the other, when most of the growth takes place,
after pod formation in summer. Very heavy flowering seems to lead to
the death of old plants, since pods are produced at the expense of
leaves. The green stems of these branches may persist in the following
year, but, often without any leaf or shoot growth and they usually die
by the end of the summer.
Small rudimentary pods begin to develop when the flower petals fall
off (generally in the first half of June). They grow rapidly and double
their length in 8 days, reaching a maximum of 60-60 mm. The seeds
in the growing pods swell to their greatest capacity and then become
hard and dry. The pod valves also dry and finally dehisce with a sharp
crack, flinging the seeds to distances up to 1.2 m. Usually pods dehisce
in mid July and continue to do 80 for the next two and a half months
(Parnell, 1962). The remaining pods open gradually between October
and December, they are the smallest and contain few or no seeds. By
September, some young bushes flower for the second time, but this
rarely occurs on old bushes. Thus a very small second crop of pode
appears by the first half of September. These pods remain green throughcut the winter, but by February the seeds within them degenerate as a
result of fungal infection and by March they shrivel and drop off
(Parnell, loc. cit.). As well as the more obvious aeasonal changes that
occur in the broom bushes there are also internal changes in the distribution of an alkaloid called Sparteine, which is characteristic of Samthamnus aqarizce (Smith, 1900b). The distribution of aphids on the
host plant largely followe that of the alkaloid (p. 126).
N. WALOFF
The shrub is a much branched perennial and according to Mr D. F.
Fourt of the Forwtry Commission (pers. comm.) and to our own observations i t haa a lifo span of 10-15 years. The older bushes are especially
susceptible to stress caused by excessive flowering and ripening of
seeds, unusually severe winters and insect attack.
The green twigs are glabrous and 6-angled and the leaves, which are
small, appear in spring and may start falling as early aa the middle of
September. In early spring the bushes may form delicate leaves a t the
beginning of February, but these are usually killed by frost and new
foliage d.evelops a month or more later. The lower leaves are shortly
stalked and consist of 3 small obovate leaflets. The upper leaves are
single and sessile. Flowers may appear as early aa in the middle of March,
but full flowering usually takes place in May. However, its intensity and
time varies from year to year. The flowers are large, bright yellow and
occur singly or in pairs. These are borne on slender pedicels in the axles
of the old leaves, forming handsome leafy rtmmes along the upper
branches. When in flower, broom attracts a great variety of insects.
There are two main growth periods in the year, one in spring just
before flowering and the other, when most of the growth takes place,
after pod formation in summer. Very heavy flowering seems to lead to
the death of old plants, since pods are produced at the expense of
leaves. The green stems of these branches may persist in the following
year, but, often without any leaf or shoot growth and they usually die
by the end of the summer.
Small rudimentary pods begin to develop when the flower petals fall
off (generally in the first half of June). They grow rapidly and double
their length in 8 days, reaching a maximum of 60-60 mm. The seeds
in the growing pods swell to their greatest capacity and then become
hard and dry. The pod valves also dry and finally dehisce with a sharp
crack, flinging the seeds to distances up to 1.2 m. Usually pods dehisce
in mid July and continue to do 80 for the next two and a half months
(Parnell, 1962). The remaining pods open gradually between October
and December, they are the smallest and contain few or no seeds. By
September, some young bushes flower for the second time, but this
rarely occurs on old bushes. Thus a very small second crop of pode
appears by the first half of September. These pods remain green throughcut the winter, but by February the seeds within them degenerate as a
result of fungal infection and by March they shrivel and drop off
(Parnell, loc. cit.). As well as the more obvious aeasonal changes that
occur in the broom bushes there are also internal changes in the distribution of an alkaloid called Sparteine, which is characteristic of Samthamnus aqarizce (Smith, 1900b). The distribution of aphids on the
host plant largely followe that of the alkaloid (p. 126).