Bs, 
-_ 
PHYSIOLOGICAL STIMULI AND ITS SIGNIFICANCE 281 
Hammer abn. N. was forced into flowering in the latter part of Janua- 
ry in the hot, humid glasshouse. The proportion of the different kinds 
of pollengrains in this inflorescence did not differ from the proportion 
in the other non-forced inflorescences. It struck us however, that many 
of the plurinuclear pollengrains had begun to germinate inside of the 
still un-opened anthers. 
Comparison between the pollen of this latter inflorescence and that 
of the other ones consequently shows that forcing at a late stage of de- 
velopment does no longer influence the proportion between the different 
kinds of pollengrains. 
Extraordinarily interesting was the sight of the pollengrains of Yel- 
low Hammer abn. W. No matter which flower or which anther was exa- 
mined, normal, fertile, pollengrains were always much in the minority. 
In some cases they were quite absent. The large, globular pollengrains, 
full of starch, always occupied, together with the plurinuclear grains, 
most of the room in the field of vision. Between these, sterile pollen- 
grains of all shapes and sizes floated. The plurinuclear pollengrains, 
especially those, which occured in the inflorescence forced into flowe- 
ring, simultaneously with the one just mentioned of Yellow Hammer 
abn. N. in the hot, humid glasshouse, had often more or less completely 
germinated, forming a wide, bladderlike tube. In a drop of methyl- 
-green-acetic acid, but also in a drop of plain water, frequently 4 or mo- 
re globular nuclei — usually 4 — were visible. In a drop, consisting of a 
diluted solution of iodine-potassium iodide the behaviour of the large 
globular pollengrains was especially striking. Their starch grains stai- 
ned immediately blue-black and as the pollengrains were stuffed full 
with them, the contours of the starchgrains were lost after staining and 
these pollengrains floated as large, black globes in the preparation, 
Whenever such a globular body bursted, the whole field of vision be- 
came filled by the escaping starchgrains. (Cf. the description of the cor- 
responding abnormal pollen of the variety Nimrod on p. 1125 of publi- 
cation 19210). 
The anthers were hardly ever so well developed as those of plants 
treated normally. In connexion with the presence of so large a number 
of sterile pollengrains, they usually had a smaller circumference and 
consequently a somewhat ribbonshaped aspect. Consequently it was 
usually possible to draw conclusions as to the quality of the pollen- 
grains, from the external aspect of the anthers. 
