32 
FRED. ELFVING, 
boundaries of the nuclei ; these, however, disappear soon, 
and the protoplasm then appears altogether homogeneous in 
the whole Pollen-body. 
The central nucleus now divides (figs. 87 — 89). One of 
the sister nuclei is larger, and has a distinct nucleolus ; 
the other is like those in the point, and, like these, has a 
small nucleolus. The three small nuclei are gradually ab- 
sorbed after this division ; they take colour in carmine solu- 
tion, gradually less and less, and finally disappear alto- 
gether (figs. 90 — 92). As the two remaining nuclei often 
show several nucleoli, one might perhaps conjecture that 
here it is not a resorption of the smaller but a conjugation 
of the larger with the smaller nuclei that takes place, such 
as is the case in the embryo-sac. Observation, however, 
shows that several nucleoli may be already present before 
the small nuclei are absorbed. 
Of the two nuclei which are now present, the one pro- 
vided with the smaller nucleolus finally divides again 
(fig. 93) ; so that we have definitely three nuclei. One 
larger, with distinct nucleolus, and two small, which 
generally have either none or a very small nucleolus 
(fig. 94). 
When these divisions have been accomplished the Pollen- 
body has become ripe. The extine has become clearly dif- 
ferentiated, and the contents inblude starch granules, and 
sometimes one finds ripe Pollen-bodies which appear to have 
two cells (fig. 98) ; closer examination, however, shows 
us that we have not here to do with a cell division in the 
usual sense of the word. The partition wall has rather 
been formed by an accidental fusion of peculiar inner 
thickenings of the intine, which is normally somewhat 
strongly developed in the apex of the Pollen-body (figs. 95 
— 97). In one instance I observed a nucleus in this so- 
formed chamber, which nucleus was clearly one of the three 
originally lying in the apex ; its resorption had been pre- 
vented by the early formation of the partition w’all. 
The Pollen tubes (5 — 10 per cent., 5 hours) always grow 
either from the base or from the side of the Pollen-body, 
never from the apex. The nucleolus of the large nucleus 
vanishes at this time, so that it can only be distinguished 
by its size, and, in most instances, by its clearer colouring 
from the two others. All three suffer a diminution in size. 
The nuclei do not go into the tube in any particular order. 
In most cases, perhaps, it is the large nucleus which goes in 
front, and it is often elongated (figs. 99, 100). But other 
combinations may take place (figs. 101, 102). 
