240 DUPLICATION OF GENERATIVE NUCLEI BY MEANS OF 
Readily admitting, that the first words only about the probable mo- 
de of development can be said, that complete cytological proof is not 
yet available — see below — I lean, after mature reflexion, towards the 
following opinion: 
Heterotype and homotype division proceed normally, the abnormal 
_ circumstances to which the plants have been exposed — one remem- 
bers the cases of Yellow Hammer abn. N. and abn. W. — notwithstan- 
ding, so that normal tetrads, each in the possession of a haploid nu- 
cleus, are formed. The physiological stimulus, to which the flowerpri- 
mordia for the next season are exposed inside of the bulb, influences 
however the further development of the tetradcells and their nuclei. It 
sharpens the struggle of existence between the tetrads. While it im- 
peaches the further existence of, frequently a large, part of the tetrad- 
cells it furthers excessive development of another part, not influen- 
cing that of the rest. 
If we accept this view, the influence of the physiological stimulus 
will be made clearer to us, if we tabulate its possible effects as follows: ” 
A. the tetrad nucleus does not reach the division-stage . . . . 1°. 
DEN , does reach the division-stage 
a. but one longitudinal splitting of the chromosomes occurs 
«no generative cellis formed! ee Zee CR eee 
B. a genérative.cellss formed. 2.0... 2. m, Sand 
b. more than one longitudinal splitting of chromosomes occurs 
«no generative.cell is formed”. wetn PNR 
6. a generative cell is formed . . . ... Sy SOR 
The numbers 1°—6° correspond to the ones fa at the beginning of 
this chapter. 
The observed effects were: 
1°. Small, tetrahedical and ellipsoidal sterile pollengrains ; these died al- 
ready at an early stage; the whole tetrad is not always affected, 
as can be deduced from the sticking of these small grains to fertile 
ones. 
2°. Pollengrains with 2 haploid, globular nuclei, corresponding to the 
vegetative nucleus of normal fertile pollengrains. 
3°. Large, ellipsoidal sterile pollengrains; they died at alater stage than 
the ones mentioned sub 1°. 
4°. Normal, fertile pollengrains. 
5°. Pollengrains with more than 2 haploid, globular nuclei, the great 
