1300 
transitions outlined above of a normal aspect to NEmec's phenomenon 
likewise manifested themselves most in the categories C and J. 
As I had acquainted myself as carefully as possible with the 
circumstances under which the plants belonging to the 13 categories, 
had lived, from the moment when the bulbs were dug up in 1918 
till the moment when the pollen was examined by me, it was not 
difficult for me to decide under what conditions of culture hyacinth- 
varieties are able to produce pollen that exhibits Nemxc’s phenomenon. 
It may be considered as a well-known fact, that the growers dig 
up their hyacinth-bulbs after the leaves have died off, towards the 
end of June and in July, then lay the bulbs in artificially heated 
barns to be dried, and plant them again in September. So, for 
instance the bulbs, — I mention this in outline only — which were 
classed by me under category D; were dug up in 1918 between 
July 1 and July 25. The barn was heated from August 1. till 
November 1, during the first weeks to 65° F., afterwards the tem- 
perature was allowed to rise to 75° F. Between September 20 and 
November 1 the bulbs were planted again. 
All bulbs which (1) were treated in this way, be it that duration 
of heating and degree of heating diverged a little, besides others 
which (2) were housed in barns where there was no heating; (3) 
were not dug up, so passed the resting-time outside; (4) were not 
planted or placed upon glasses; (5) were cultivated on glasses; (6) 
differed in age or size, never produced flowers the pollen of which 
showed Némec’s phenomenon. It was different with those plants 
which partially had suffered what is called “preparation”. The bulbs 
chosen for that purpose, are dug up in an unripe state, heated pretty 
strongly in the barn, and afterwards planted in pots or placed upon 
glasses. When the bud begins to rise a little above ground, the 
plant is exposed to a higher temperature a second time, the conse- 
quence of which is that the flowers bloom very early. See for this: 
A. H. Braauw: On the periodicity of Hyacinthus orientalis p. 51, 
Vol. XVII of the “Communications of the Agricultural University”, 
and my publication: “On the occurrence of heteroploid varieties of 
Hyacinthus orientalis L. in the Dutch cultures”. Arch. Néerl. 1921 
and Genetica 1921. 
So the bulbs of the variety Nimrod (category B) in the flowers 
of which 1 first. found pollen-grains which showed me NEmEc’s 
phenomenon, were dug up on June 10%, the leaves still being a 
fresh green not showing a trace of dying off. 
They were exposed for 21 days to a temperature varying on an 
indented line from 90° F. to 78° F.; afterwards till October 26 to 
