280 Beer,— On the Development of the Spores of Ricci a glauca, 
hand, calcium-chloride-iodine and chlor-zinc-iodine do not stain these layers. 
In ruthenium-red and bismarck-brown they assume a faint colour, but I do 
not think that this is sufficiently marked to indicate the presence of pectose 
in these layers. 
The membranes which first limited the cells of the tetrad from one 
another before the thickening layers were deposited can now be seen as 
middle lamellae running through the midst of the callose layers, and as a 
peripheral covering to the entire tetrad. These primary membranes con- 
tinue to colour distinctly pink-violet with calcium-chloride-iodine solution 
and deeply red with ruthenium-red, whilst callose reagents leave them 
unstained. They still possess, therefore, the unchanged pectose-cellulose 
constitution which they had in the first place. 
It may be mentioned here that Leitgeb 1 reached very different results 
on these points. During the earlier stages following the thickening of the 
special-mother-cell walls he could distinguish no middle lamella, and only 
after the first spore-wall has made its appearance ‘ differenzirt sich in den 
Scheidewanden die Mittellamelle.’ This is certainly incorrect, for the 
middle lamellae are nothing but the original pectose-cellulose septa of the 
unthickened special-mother-cell wall which maintain their individuality 
throughout. 
Leitgeb further states, on the same page, that in aniline-blue an outer 
layer of the special-mother-cell wall colours deep blue whilst the inner 
parts, corresponding to our secondary thickening layers, only assume a 
yellowish tinge in this solution. If this were the case we should have to 
conclude that the composition of the special-mother-cell wall is very 
different from that which I have described above, but I have so repeatedly 
assured myself that the behaviour of this wall towards aniline-blue is pre- 
cisely the opposite to what Leitgeb found and, moreover, this has been so 
thoroughly supported by the reactions of the wall with other reagents, that 
there cannot be the slightest doubt of the correctness of my conclusions. 
The occurrence of callose in the special-mother-cell walls of one of the 
Hepaticae is of interest since in no other member of the Archegoniate 
series which I have examined is that substance to be found in this position ; 
and it is only when we reach the Gymnosperms and Angiosperms that 
callose can again be seen surrounding the pollen-tetrads 2 . 
It is very probable that callose occurs constantly in the special-mother- 
cell walls of the liverworts since some observations which I am making 
upon the spore-development of Anthoceros laevis have shown that callose 
is also present in the tetrad walls of this plant. 
In the Musci the special-mother-cell walls contain pectose and cellulose, 
1 Leitgeb, 1. c., p. 43. 
2 In all Gymnosperms and Angiosperms which I have examined callose formed the only 
demonstrable constituent of the special-mother-cell wall. 
