28 1 
Beer —On the Development of the Spores of Riccia glanca. 
whilst in the leptosporangiate ferns* the Ophioglossaceae and in the ligulate 
and eligulate Lycopodiums these walls contain either cellulose and pectose 
or pectose alone, but no trace of callose 1 . On another occasion 2 I have 
referred to the manner of origin of callose in the special-mother-cell walls 
of Oenothera , and the same remarks apply with equal force to the callose 
of Riccia. In the present case it is impossible to suppose that the callose 
can have arisen from the transformation of cellulose, since none of this sub- 
stance precedes the callose nor can any cellulose be seen to disappear from 
other neighbouring membranes. We must conclude, therefore, that the 
callose in the tetrad walls of Riccia is formed directly as such by the 
protoplast. 
The tetrad-group grows in size from about 6 o/x to about 75 to 85 /x in 
diameter and then the first spore-wall 3 is formed round each of the four 
cells. The question of the origin of this layer constitutes one of the chief 
points of difference between the accounts of Leitgeb and Strasburger. The 
former writer was convinced that this wall is a transformation product of 
the innermost layers of the special-mother-cell wall, whilst Strasburger is 
equally positive that it is a new formation of the protoplast which has no 
relation to the special-mother-cell wall. 
I have spent no little time upon this question and the only conclusion 
which I am able to reach is a negative one. After carefully considering the 
grounds upon which Leitgeb and Strasburger based their respective views 
I am forced to conclude that these were insufficient to prove the case either 
one way or the other. Leitgeb lays the greatest weight upon the firm 
adhesion which exists between the special-mother-cell wall and the first 
spore-wall. After treating the spores with various reagents (chlor-zinc- 
iodine or a not too strong mixture of chromic and sulphuric acids) he found 
that the first spore-wall remained firmly fixed to the special-mother-cell 
wall, although this was greatly swollen. 
An argument based upon the adhesion of two layers to one another 
cannot, however, be accepted as proof of their common origin. Cases are 
known in which two layers are firmly united but which have unquestionably 
been separately deposited by the protoplast. Thus Fitting 4 has referred 
to the special-mother-cell wall and the secondary thickening layer of the 
spore-mother-cell wall of Isoetes which adhere closely together but which are 
independently developed. The special-mother-cell wall and the very young 
pollen-wall of the Phanerogams furnish another example of two layers which 
1 I have, unfortunately, had no opportunity of examining the special-mother-cell walls of 
Equisetum as yet. 
2 Beer, 1 . c., p. 290. 
3 In the following account I have avoided the terms exospore or perispore and speak only of 
first and second spore-membranes. Since, however, the innermost layer of the spore is certainly 
homologous with the endospore of other plants I have used that name for it, 
4 Fitting, H., Bot. Zeit., Bd. 58, 1900, p. 126. 
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