294 Beer, De\ T elopment of tlie pollen grain and antlier of some Onagraceae. 
red leaves it unstained. Methylene-blue and fuchsin mixture 
stains tlie layer pink or violet. 
I have found tliat tlie first pollen-wall of tlie Horse- 
chestnut in its early stages, gives reactions which are almost 
identical with those of tlie secondary layer of Oenothera. Apart 
from tlie very striking violet reaction with. tlie lodine solution 
tlie properties of fliese menibranes correspond fairly well with 
those characteristic of pectic substances and it is not improbable 
that we are here dealing with an association between a pectic 
body and a snbstance of nnknown nature. Additional support 
is given to this view by the fact that the violet reaction be- 
comes lost after treatment of the pollen grains with absolute 
alcohol, no doubt because the body which gives this reaction 
is soluble in alcohol. In its behaviour towards other reagents, 
however, the thickening layer remains unaltered after an immer- 
sion in alcohol. Cuticularisation takes place very early in these 
membranes 1 ) and the violet-reacting body may he associated 
with the first stages of this process. 
In alcohol material the thickening layer, at the early peri- 
ods of its development, is often greatly swollen 2 ) and this be- 
comes more marked and may even lead to the bursting of the 
pollen grain if this be examined in aqueous Solutions. 
The interstitial body is now 3 ) limited towards the cavity of 
the grain by a closing disc which has the same composition as 
the rest of that body although it is somewhat denser. The 
reactions of the whole interstitial body have undergone a change 
and are no longer those of a pure pectic body. With Iodine- 
reagents it colours yellow; with congo - red it stains uniforraly 
red; with naphtol black it colours blue-black; with nigrosin it 
becomes black; with ruthenium red it stains red; with methylene 
blue-fuchsin mixture it colours blue, pink or violet according to 
the strength of tlie solution used; with corahin-soda solution it 
remains colourless. 
The protoplast hlls the cavity of the pollen grain at this 
stage but weak plasmolysing agents show tliat, whilst it is firmly 
fixer! to the developing secondary layer, it is free from the bases 
of the interstitial bodies. 
As the thickening layer of the pollen wall continues its 
development ring-shaped ridges make their appearance at the 
bases of the interstitial bodies. These are at first low and in- 
conspictious but soon become sharp and prominent features on 
the membrane (Figs. 23 and 24). 
In pollen grains of Oenothera longiflora 3 ) which measure 
!) After which they colour yellow to brown with Iodine in potassium 
iodide solution. 
2 ) This was already noticed by Strasburg er in Gaura biennis. 
3 ) Pollen grains measure at this time 35 to 38 u in Oenothera biennis 
and 0. longiflora. 
3 ) Although I give here the actual description and measurement of 
the pollen of Oenothera longiflora the facts are essentially the same in 
0. biennis. 
