( 190 5 
the pollen from the shorter stamens of Torenia, the stigma opens 
again, and not when that from the longer is taken, may likewise 
be referred to the difference in the ratio of water of these grains. 
If the pollen from the closed shorter stamens is collected on an 
piece of glass and exposed to the air for some time until, by loss of water, 
it has assumed the elliptical shape, it acts in the same way as that 
of the longer, and if, inversely, that of the longer stamens is used 
when these have not yet opened, it behaves on the stigma like the 
pollen from the shorter. 
Finally, to determine whether both species of pollen possess the 
faculty of absorbing water in an equal degree, pollen of Torenia 
was put on the stigma of Mimulus, and inversely, that of Mimulus 
on the stigma of Torenia. It appeared now that the stigma of . 
Torenia remained closed when dusted with pollen of Mimulus; 
inversely, however, the stigma of Mimulus opened again after being 
dusted with pollen of Torenia, whence it is evident that the power 
of absorbing water is greater in Mimulus than in Torema. 
In reference to an earlier paper on contrivances on the stigma to 
prevent the germination of foreign pollen, in which it was inferred 
that for some plants the pollen-grains want a special chemical stim- 
ulus in order to form their germinal tubes, I will now call to 
mind, in accordance with what has been mentioned above, how also 
the concentration of the stigmatic fluid should be considered as a 
means to prevent the germination of foreign pollen. 
Torenia and Mimulus have hardly any chance of foreign pollen- 
tubes developing on their stigmas. The composition of their stigmatic 
liquid warrants them from it. 
What has been stated here is by no means an isolated fact but 
should be considered as a special case in the appearance of a 
frequently occurring means to prevent the germination of foreign 
pollen. Accordingly, in many cases it explains the phenomenon men- 
tioned by STRASBURGER ') that very often the pollen of closely allied 
plants cannot germinate on each other’s stigma, whilst foreign 
pollen does. 
The description of a few more experiments will nearer elucidate 
this point. | 
The pollen of Impatiens sultani, I. Balsamina, and J. latifolia, 
belong to those kinds which easily germinate in distilled water. 
1) SrrasBURGER, Ueber fremdartige Bestäubung. Pringsheim’s Jahrb. für w. Botanik, 
Bd. XVIII, 1886. 
