202 Beer . — Studies hi Spore Development. 
The tetrads of young pollen-grains become surrounded by massive 
mucilaginous walls. Upon the periphery of each tetrad group is a granular 
deposit which stains with Bismarck brown but not with aniline blue or 
corallin soda. This is probably the remains of the primary wall which 
separates the sporogenous cells from one another. Within this a distinct, 
often rather massive, layer is seen which possesses the staining properties 
characteristic of Mangin’s callose and of pectose. 1 This is the mother-cell 
wall already referred to above. Within this again is another mucilaginous 
wall which also gives the reactions of callose and pectose and which envelops 
the young pollen-grains and separates them from one another. For this 
innermost wall Strasburger ( 19 ) has recently suggested the convenient 
name of Special wall to replace the old term Special mother-cell wall with 
its false implication (Fig. 2). 
In microtome sections which have been stained either with aniline blue 
or Congo red three radiating lines (really lamellae), often of a granular 
appearance, can be seen to traverse the middle of the special wall (Fig. 2). 
These granular bands are the first lamellae which are formed at the 
conclusion of the division of the mother-cell. In my sections stained with 
Heidenhain’s iron-alum haematoxylin and Bismarck brown these lamellae 
are often quite unstained and appear as colourless clefts or lines in the 
middle of the brown special wall. Mangin ( 11 ) has described similar tri- 
radiate lines of granules in the case of Althaea rosea , and he states that they 
are nitrogenous in character. I was unable to determine their chemical 
nature in the case of Ipomoea. 
At the time when the callose-pectose walls break down and set the 
pollen-grains at liberty it is often seen that the triradiate lamellae continue 
to exist for some time in the midst of the flocculent material derived from 
the rest of the wall (Fig. 3). 
The callose-pectose layers of the special wall which immediately envelop 
the pollen-grains and which are the latest parts of this wall to be formed 
are denser than those in the neighbourhood of the granular lines. 
There is evidence that the special wall of Ipomoea possesses a laminated 
constitution. 
The young pollen-grains of Ipomoea surround themselves with a wall of 
their own — the exine. This is deposited by the pollen-protoplast as an 
extremely delicate layer upon the inner face of the callose-pectose wall 
which surrounds it. From the first it is marked off as an independent 
structure from the callose-pectose special wall, and there can be no doubt 
that it is a new membrane and not one derived from the transformation of 
the innermost lamellae of the special wall. 
In its earliest stages it is an exceedingly delicate membrane, which 
is too thin to permit any structure to be seen in it even with the highest 
1 Compare Tischler (21), p. 48 . 
