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Impatiens sultani, for instance, can do this from solutions of 
0—_20 pCt., J. balsamina vof O— 10 pCt. and J. latifolia of 0—8 pCt. 
Beneath the limit mentioned for each species they are al! three able 
to form their germinal tubes; above that limit the germination 
ceases, together with the absorption of water and the accompanying 
increase of volume. 
In the same way as the pollen behaves towards saccharose solu- 
tions, it behaves towards the fluid of the stigma, and now it is my 
opinion, that as a rule it may be admitted that pollen, which does 
not besides put special requirements to the qualitative composition 
of the stigmatic fluid (of which my paper in the Meeting of 
September 29, 1900 treats), can only then germinate on a stigma 
when the concentration of the stigmatic liquid does not exceed 
a certain maximum, varying for each species of pollen. 
The fact, now, that the stigmas of Torenia and Mimulus open 
no more after being dusted with their own pollen (Torenia with 
the pollen from the longer stamens) should be ascribed to the 
faculty of these kinds of pollen to withdraw considerable quantities 
of water from the stigmatic fluid of those two plants. 
This withdrawing of water is the factor which counteracts the 
restoring of the turgor. | 
Direct observation taught me that none of the other pollen species 
with which experiments on fertilisation had been made possess 
the same property. 
If the elliptical pollen of Hemerocallis fulva, Maurandia erubescens, 
Digitalis purpurea, or Lupinus Cruykshanksii, is put on the stigmas 
of Mimulus or Torenia, and if it is again examined after the stigmas 
have reopened, it is seen to have retained the shape which it possessed 
in the dry state; none of the grains has been able to become globular. 
The pollen of Torenia, on the other hand, also elliptical as 
long as it is dry, and that of Mimulus, which on the optical section 
shows an oblong square, is. directly after the stigma has closed 
found back between the lobes strongly swollen and rounded into balls. 
That this is indeed the explanation of the observed phenomena 
is shown by control experiments. In the first place we see that when 
the stigma of Torenia or Mimulus, is covered with pollen which 
beforehand has been enabled to absorb water and become globular, — 
simply breathing over the pollen will suffice to this end, — this 
pollen acts in the same way on the stigma as foreign pollen, namely, 
as concerns the reopening of the lobes. Just the same is seen to 
occur when the stigma, previously to the fertilisation, is moistened 
by means of a pulverisator. Furthermore the fact that, when using 
