Bu 
PHYSIOLOGICAL STIMULI AND ITS SIGNIFICANCE 239 
tive nuclei, are composed, just, as the nuclei of the somatic cells of these 

Fig. 2. 
Fig. 2. Camera lucida drawing of the nucleus of mikrophoto n°. 8. Explanation 
see there. The numbers 1—4 indicate the long chromosomes; 5—6 those of me- 
dium size and 7—8 the small ones. 1050 approximately. 
varieties, of 16 chromosomes, 8 of which are long, 4 of which are of medium 
size and 4 of which are small. 
VI. CAN A CONNEXION BE DEMONSTRATED BETWEEN THE VERY DI- 
VERSE HABIT OF-THE POLLENGRAINS AND THEIR DEVELOPMENT? 
The occurrence in the same anther of: 
1°. small tetrahedical and ellipsoidal sterile pollengrains ; 
2°. pollengrains, provided with two haploid, globular nuclei ; 
3°. large, ellipsoidal, sterile pollengrains ; 
4°, normal, fertile pollengrains ; 
5°, pollengrains with more than two haploid, globular nuclei; 
6°. large, globular, diploid pollengrains ; 
raised the important question whether a logical explanation for these 
simultaneous occurrences could be found. 
This seems to me the more important, as some investigators, per- 
haps under the suggestion of certain existing hypotheses, connect the 
origin of diploid sexual nuclei in the case of diploid plants, without fur- 
ther consideration, with the dropping out of the reduction-division. 
It seems to me however, in connexion with the simultaneous pre- 
sence of the different kinds of pollengrains enumerated sub 1°—6°, 
that a close relation between their origin must exist, and that this rela- 
tion can best be sounded, if we imagine a normal reduction-division to 
occur. 
