( 187 ) 
ively due to the thereby nearly unavoidable touching of the irritable 
inner surface. 
If very cautiously a quantity of pollen is shedded on the stigma, 
so that the grains adhere to the stigmatic hairs, the lobes remain 
open; if it is effected more or less rudely, so that the cellular tissue 
is touched, they close. 
What has been stated here about the closing in consequence 
of some mechanic stimulus, and the again opening of the stigmatic 
lobes when that stimulus has ceased to act, clearly points to the 
fact that the irritable stigmas, in their movements, show many 
points of accordance with what has been observed in other ir- 
ritable organs, for instance, in the articulations of the leaves of 
Mimosa pudica, the stamens of Centaurea jacea, and other Cynareue, 
so that by analogy it may be admitted, that touching the inner stig- 
matic surface is accompanied by a loss of water in the turgescent 
cells at that place, in consequence of which the cell-layers at that 
side lose their tension, whilst that at the outside increases by the 
absorption of a part of the expelled water. Hence, the tension of the 
outer side becomes greater than that of the inner one which explains the 
closing of the lobes. 
When now the stimulus has ceased to act the flaccid cells at the 
inner face again absorb water, by which the turgor is restored and 
the lobes reopen again. 
Hence it follows that the reopening of the stigmatic lobes, after 
they have been temporarily closed by only touching or by covering 
them with pollen, may be referred to well-known phenomena, but 
that the not opening of the lobes when pollen is shedded on them, 
of the same species (Mimulus), or from special stamens of the same 
species (Torenia), requires some explanation. It is clear that here, in 
dusting a stigma with this special pollen, a factor appears which 
prevents the restoring of the turgor. 
In order te explain this phenomenon it should be observed 
that the stigmatic fluid of different plants not only varies in qualit- 
ative composition, concerning which some particulars were given in 
the account of the Meeting of Sept. 29, 1900, but that, besides, 
to all probability, the different constituents of this fluid can occur 
in varying proportions; that the concentration of the stigmatic fluid 
can vary very much, and that pollen-grains of distinct origin diverge 
considerably in their power of drawing water from one and the 
same stigmatic fluid. The latter fact may at once be seen by put- 
ting pollen of distinct plants in a solution of saccharose of a 
