PHYSIOLOGICAL STIMULI AND ITS SIGNIFICANCE 237 
It was now much easier to study the contents of the anthers and of 
the pollengrains. In the sterile pollengrains a dead nucleus could often 
be observed. 
The few normal, fertile pollengrains showed nothing out of the way. 
They possessed, as usual, a globular vegetative nucleus. Within the 
generative cell, which, depending on the stage of development, had 
either separated itself, by means of a wall of the shape of a watchglass, 
at one of the most curved extremities, from the vegetative cell or was 
lying, as a spindle-shaped body, near the vegetative nucleus, a genera- 
tive nucleus was present which had the shape of a longitudinally stret- 
ched ellipsoid. The longest axis was sometimes 6 tot 7 times as long as 
the small axes were. The vegetative nucleus, was, owing to the greater 
laxity of the chromatine, stained lighter than the generative one. 
Besides the many sterile and the few normal fertile pollengrains, ab- 
normal plurinuclear and large globular ones, especially, were present. 
About the plurinuclear pollengrains the following was ascertained: 
As I had chosen the anthers of the Yellow Hammer abn. W. forced 
into flower in the warm, humid glasshouse, many of the observed plu- 
rinuclear pollengrains had already sprouted. (Cf. Chapter III). 
Frequently the nuclei had entered already into these tubes, where 
they could easily be observed. In size and shape they could always best 
be compared with the vegetative nucleus of a normal, fertile pollen- 
grain. In most cases 4 of these nuclei were present, but 5—8 have been 
observed; there were also pollengrains with 2 such nuclei. The abnor- 

Fig. 1. 
Fig. 1. Camera lucida drawing of the pollengrain of mikrophoto n°. 5. Expla- 
nation see there. In the two nuclei at the extreme left of the drawing no nucleolus 
could be observed. x 525 approximately. 
mality consequently consisted in the facts, that the two nuclei present 
were globular, that they were not separated by means of a cell wall, 
that the pollentube, when present, was distended and that the exine 
