Beer, Development of the pollen grain and anther of some Onagraceae. «'301 
itself and the pollen-wall and, in all probability, the latter derives 
the necessary materials for its growth from this source. 
Unfortnnately I could gain no knownledge whatsoever of 
the Chemical natnre of this liquid. 
In the tapetum we can also observe evidences of metabolic 
activity but I can find nothing to show that any of the material 
which is being formed there is leaving the cells, on the con- 
trary there is reason to believe that an accnmulation of sub- 
stance is taking place. 
In the very young pollen grain 1 ) the first wall appears as 
a single homogeneous lamella bnt when the grain has grown 
and measures abont 40 y across we can indistinctly recognise a 
structural differentiation in the outer membrane. 
When the diameter of the pollen grain has increased still 
further (to abont 55 to 60 y) its first membrane can be clearly 
seen to consist of a thin, outer homogeneous layer and an inner 
“rodlet“ layer (Stäbchenschicht or Anschlußlamella 2 ). 
The growth of this membrane recalls Strasb urger 's 3 ) 
description of the first pollen-wall of Älthaea rosea which, at a 
certain stage, was seen to consist of three lamellae: a middle 
“rodlet“ layer (Anschlußlamella) which is bounded peripherally 
by two homogeneous layers. Of these the innermost lamella 
soon ceases to grow and becomes gradually more attenuated 
until it is lost sight of altogether; the two otlier lamella increase 
in thickness and the “rodlets“ can be very clearly studied in 
older stages. A thickening layer is *developed within the first 
pollen membrane of Älthaea. 
In Oenothera the first wall is so thin during its early deve¬ 
lopment that I have not been able to determine whether the 
“rodlet“ layer is ever bounded internally by an inner homogeneous 
lamella; it is certain, however, that by the time the pollen grain 
has reached 55 to 60 y in diameter every trace of it has vanished. 
The first pollen-wall now grows more rapidly in surface 
than the secondary thickening layer beneath it and consequently 
it becomes separated from that layer at all parts and only re- 
mains firmly fixed to the interstitial bodies. The continuation of 
this unequal growth in surface gradually throws the outer wall 
into irregulär and sinuous folds. Both primary and secondary 
layers of the wall have meanwhile undergone a change in their 
Chemical Constitution and have become more or less completely 
cuticularised. The secöndary layer no longer gives a pure violet 
colour with a solution of lodine in potassium iodide but this 
has changed first to a violet - brown and then to a pure brown 
reaction. 
x ) This description of the pollen-wall applies both to Oenotli. longiflora 
and to Oen. biennis nnless specially stated to the contrary. The measnre- 
ments more particnlary refer to 0. biennis bnt the dimensions are only very 
slightly, different in O. longiflora. 
2 ) Strasbnr ger, “Die pflanzlichen Zellhänte“. (Pringsh. Jalirb. f. wiss 
Bot. Bd. XXXI. 1898. p. 551.) 
3 ) 1. c. p. 555. 
