PHYSIOLOGICAL STIMULI AND ITS SIGNIFICANCE 255 
If me now remember, that it were exactly those conditions, under 
which duplications of generative nuclei takes place in practical cultiva- 
tion, which we applied in our efforts to obtain them experimentally, 
it is no wonder, that further enquiries and investigations showed us, 
that the cause of the origin of triploid forms in the Dutch cultivations vs 
exactly the same as the cause of the origin of those forms in our experiments 
e.g. in all probability fertilisation of haploid eggcells by duplicated sperm- 
nuclei. 
Our enquiry began by a study of the methods of cultivation which 
had been applied in the course of the centuries. It had to be investiga- 
ted whether in former times, as now, the breeding took sometimes pla- 
ce under external conditions, favoring — as we now know — duplication 
of generative nuclei. I now think that such has really taken place. In 
order to form an opinion about this point the external conditions in 
question must be remembered and kept in mind. 
Bulbs which have been taken up in an unripe condition e.g. while the 
leaves were still green or partly green, produced inflorescences with the ab- 
normal pollengrains mentioned (Cf. point IV of publication 19210). 
This taking up of the unripe bulbs is the first phase of the so called 
preparation of the bulbs, which embraces: 
1°. the taking up of the bulbs before the 14th of June; 
2°. the exposing of the bulbs to artificial heat during some weeks; 
3°. the making them root in a cool surrounding ; 
4°. the forcing them into flowering towards winter by means of artifi- 
cial heat. 
We notice at once the similarity of this „preparation” with the 
treatment, to which Yellow Hammer abn. N. and abn. W. have been 
submitted (Chapter II). The harvesting of the bulbs in an unripe con- 
dition must be considered as the chief-cause of the duplication of the 
male generative nuclei, as results from the investigation of the mate- 
rial in 1919 and the experiments following upon this investigation. 
In how far the subsequent exposure of the bulbs to artificial heat, 
influenced the result, cannot be made out with certainty, the less so, as 
abnormal fertile pollengrains were also observed in flowers, the bulbs 
of which had only been submitted to the first phase of preparation . 
In this connexion the conclusions, formulated by Blaauw (1920) 
should be mentioned: , The earlier one applies dry Heat, the earlier the 
