This section is from the book "Commercial Gardening Vol2", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
The best-known kinds are capensis, with narrow leaves and spikes of whitish flowers, and selaginoides, having white flowers with an orange centre. Both kinds are South African annuals, and are raised from seeds sown in heat in spring. N. lychnidea is a tender hairy perennial 6-12 in. high, with spikes of yellowish-white flowers in summer.