PHYSIOLOGICAL STIMULI AND ITS SIGNIFICANCE 265 
„Am Ende aller Enden entscheidet schliesslich nicht die Spekulation 
sondern einzig und allein das Experiment”. 
This, for the present, ist the only fitting answer to this question, 
which is of so great an importance in connexion with the evolution- 
concept. 
RESUME 
1. It has been shown that in the case of varieties of Hyacinthus orien- 
talis, both in such with single and in such with double flowers, ab- 
normal, and in all probability fertile, pollengrains can be produced 
by means of physiological stimuli. 
2. This can be done as well in the case of diploid, as in that of hetero- 
ploid, varieties. 
3. These pollengrains deviate frequently from the normal ones by 
their globular shape and great size, the normal ones being ellipsoi- 
dal and smaller; in this case, they are, when occurring in diploid 
varieties, characterised by the possession of a vegetative nucleus 
and one or two generative nuclei, all possessing the double volume 
of the nuclei, corresponding to them, in normal pollengrains ; from 
this, and from the number of chromosomes observed during karyo- 
kinesis, it follows, that these pollengrains, occurring in diploid va- 
rieties, are diploid themselves. 
4. Besides this kind of aberrant pollengrains, an other abnormal kind 
always occurs, one which possesses 2 to 8 globular nuclei ; from the 
size of these nuclei and from the number of their chromosomes it 
can be concluded, that — in case of their occurance in diploid va- 
rieties — these pollengrains are haploid; they can more easily be 
induced to sprout in a cane-sugar-solution than normal pollen- 
grains and form wide, somewhat bladdershaped, pollentubes in 
such a solution. 
5. The obtention, in the experimental way, of sexual nuclei, having 
exactly twice the volume of normal sexual nuclei or the number 
of which has approximately been doubled, can be called: dupli- 
cation of sexual nucler. 
6. This duplication probably takes place after normal heterotype- 
_and homotype-division. 
7. When diverse varieties are exposed to the physiological stimuli, 
in question, they show a different susceptibility towards these 

