242 DUPLICATION OF GENERATIVE NUCLEI BY MEANS OF 
rest after the formation of the generative cell, this phase is, in ab- 
normal cases, postponed or even, never reached. The biological re- 
gulator, which acted so precisely in normal cases, has got out of or- 
der and this favors the formation of the different kinds of pollen- 
grains mentioned. 
As well as the physiological stimulus has caused, in the pollengrains 
sub 5°, numerical multiplication and, usually, duplication of generati- 
ve nuclei, so it is the cause of duplication of the size of the pollengrains 
sub 6°. Both phenomena, are comprised in the term , duplication of ge- 
nerative nuclei’’, here used. 
In the case under discussion, the following alternative interpreta- 
tion will probably appeal most to those who consider the dropping out 
of the reduction division a conditio sine qua non for the origin of di- 
ploid generative nuclei. 
The physiological stimulus makes the reduction division drop out. 
The pollenmothercell and its content are thereby transformed to large, 
globular diploid pollengrains. Pollengrains with 2 or more globular, ha- 
ploid nuclei arise, when, after reduction division, which in these cases } 
proceeds regularly, the normal development of the tetradcells becomes 
blocked. This may happen when the diad-stage has just been reached 
(in the case of the pollengrains with 2 globular haploid nuclei), in most 
cases however 4 globular, haploid nuclei are formed, but no cellwalls 
are formed for their separation. Not infrequently these nuclei divide 
again. 
In this way also, the modes of origin of these 2 kinds of abnormal 
pollengrains are brought under one point of view. A connexion of some 
kind, can, no matter how one may wish to explain the mode of devel- 
lopment, not be denied, in my opinion. p 
If we prefer this explanation, we are forced to assume, that the pol- 
lenmothercells themselves are able, to form an exine and intine and to 
germinate. Moreover, the determination of the connexion between the 
origin of these abnormal fertile pollengrains and the dying off of the _ 
younger and older normal pollengrains seems to me to be more difficult 
_in this than in that of the former attempt to explain things. Evi- 
dently both explanations are liable to modification in detail. In respect 
to the former, one might assume that the phenomenon of synhaploidy 
did not appear, before the generative cell had segregated from the 
