90 Sudden Appearance and Constancy. 
In the case of the vast majority of sterile varieties 
we know neither how, when nor where they arose. They 
are propagated by vegetative methods and have been 
from time immemorial. But they differ from their sup- 
posed parent species so markedly that they take rank 
with the best varieties. Nobody supposes that they have 
arisen gradually. 
The first instance that I give is Lilium candidum 
plenum, a form which is on the market. It is a well- 
known variety, the bulbs of which are offered every year 
by dealers in bulbs, in their catalogues. Instead of 
flowers it has long stalks clothed with petals (Fig. 13). 
The stalk is the elongated thalamus ; the petals are nar- 
row and dead white, and of the color and structure of the 
petals of other white lilies. In each flower they continue 
to appear for several weeks ; the lowest may be brown and 
withered before the uppermost have unfolded. Figure 
13 shows a fairly short flower; they are often twice as 
long. Stamens and carpels are never formed ; the apex 
consists of a compact bud of the youngest petals. 
We do not know how the variety first arose. It was 
first described by G. VROLIK in 1827, after he had al- 
ready seen it flowering for 20 years in the Botanical 
Garden in Amsterdam. 1 It is therefore nearly a century 
old. In horticultural literature it is not referred to until 
much later, about 1840. 2 
Another well-known sterile garden plant is the green 
Dahlia (Dahlia varidbilis viridiflora). The flowerheads 

1 G. VROLIK, Over ccn rankroruiige ontwikkeling van wittc Iclic- 
blocnicn. Verhandelingen der eerste klasse v. h. k. Nederl. Instituut 
van Wet. te Amsterdam, Part I, 1827, pp. 295-301, with one table. 
The spike with five flowers figured there, is still preserved in our 
collection. 
2 See MERAT, Ann. Soc. d'hortic. dc Paris, 1841-1845, and VERLOT, 
loc. cit.j 1865, p. 91. 
