1&2 
Beer . — On the Development of the Spores of 
The further growth in thickness of the exospore continues to leave the 
fold of endospore uncovered at the apex of the spore. The smooth surface 
of the exospore now becomes slightly wavy in outline, and this soon leads 
to the formation of the reticular sculpture which is characteristic of the 
mature spore. 
The fully grown spore measures, in section, about 33 m by 28 fx. The 
exospore is thicker at the apex than over the rest of the spore, but is 
perforated by a cleft through which the fold of endospore reaches the 
exterior. This cleft is particularly well seen after treatment with a mixture 
of sulphuric and chromic acids or with sulphuric acid alone, but it can be 
quite readily distinguished in sections which have been stained with 
methylene blue, or bismarck-brown without the previous action of acid. 
Chlor.-zinc-iodine solution, to which more iodine than usual has been added, 
also very clearly shows the endospore — coloured brown— penetrating the 
exospore and reaching the exterior. The reticular sculpturing upon the 
surface of the exospore appears in section as a series of blunt processes 
with flattened summits (Figs. 10 and ti). The protoplast of the spore has 
now become somewhat richer in substance and usually includes starch, 
but not in any quantity. 
Nothing in the nature of an epispore is to be found in the spores of • 
Helminthostachys. The exospore and, most probably, also the endospore 
are in the first place deposited by the secretory activity of the spore- 
protoplast. There is no possibility of the former layer being derived 
from the transformation of part or all of the mother-cell-wall, since this 
at all times very delicate wall can still be distinguished, in apparently 
undiminished thickness, over the surface of the young exospore (Fig. 6 ). 
The fact that the exospore and endospore are inseparably united 
together at first suggests the probability of the two layers being derived 
from the differentiation of an originally single, homogeneous membrane. 
As Fitting 1 has already pointed out, however, the existence of a close fusion 
between two layers of a wall does not' necessarily indicate their common 
origin by differentiation, and there are several well-known cases in which 
two lamellae are intimately bound together, but which unquestionably 
have been separately deposited by the cell-protoplast. In the present 
instance, moreover, it is difficult to understand how a cuticularized 
membrane can be so differentiated as to give rise to a pure pectic lamella 
on one of its faces. The development of the little fold of endospore at 
the apex of the spore is also more readily explained as a new formation 
than as a product of differentiation. Shortly after the exospore has been 
formed round the young spore and throughout the time that this layer is 
growing in thickness and in surface the tapetal plasmodium which 
envelops the spore-tetrads shows unmistakable signs of metabolic activity. 
1 H. Fitting, Bot. Zeitung, Bd. Iviii, 1900, p. 126. 
