(191) 
As a rule, it begins to form the germinal tubes directly after being 
laid in water, whilst other species only after 2 or 3 hours show 
the first signs of germination. In a quarter of an hour already 
the pollen-tubes have got a considerable length. Hence, that pollen 
does not want a special chemical stimulus, nor a germinal fluid of 
a higher degree of concentration. 
In dilute solutions of saccharose, levulose, dextrose, and mannite, 
it germinates as well as in water. 
How indifferent this pollen may appear, it is still far from being 
able to form germinal tubes on all possible stigmas. 
If the polien of Impatiens sultani is introduced into the thick 
viscous liquid which covers the stigmas of Uvaria purpurea, it does 
not try to form germinal tubes, and when, after residing for several 
hours in this fluid, it is again put in water, the germination leaves 
nothing to desire. If then again a portion of the viscid matter is 
put on a piece of glass and diluted with water, the pollen-grains 
of Impatiens directly begin to germinate, whence may be inferred 
that only the higher concentration prevented the germination on 
the stigma. 
If now the experiment is inverted by covering the stigma of Impatiens 
sultant with pollen of Uvaria, then, after about 24 hours, the germinal 
tubes are seen to appear. Such like cases, where the pollen of a plant 
A germinates on the stigma of B, but inversely, not that of B on 
the stigma of A, STRASBURGER has frequently called attention to. 
The above observations give a plain explanation of the phenomenon, 
though, of course, for other plants other causes may be active too. 
As little as on the stigmas of Uvaria does the pollen of Impatiens 
germinate on the stigma of Pentas carnea, Begonia goegoeënsis and 
Torenia Fournieri. It can remain for days on these stigmas without 
any change being observed. If then the stigmas of Begonia and Torenia 
with the pollen of Zmpatiens upon them are put in a drop of water, 
they will begin to form germinal tubes within a few minutes. For 
Pentas carnea, however, the high concentration of the stigmatic 
liquid is not the only cause that the pollen-grains do not germinate 
in it. After having been on the stigma of Pentas carnea, the 
pollen of Jmpatiens is dead, no matter whether it has been for 
some days, or only for a few hours in contact with the stigmatic fluid. 
This evidently poisonous influence on the pollen of Impatiens is, 
however, only exerted by the concentrated liquid of the stigma. 
If a stigma of Pentas carnea is placed in a drop of water in 
which pollen of Impatiens has been sown the germination is quite 
satisfactory. 
