88 DIVISION I.—GENERAL MORPHOLOGY. 
of the ascus is shown by the fact, that the expansion diminishes with a diminution 
in the amount of fluid in the cell and disappears, either suddenly and entirely, if the 
wall of the ascus opens spontaneously or is pierced artificially and the fluid escapes, 
or gradually through the slow operation of alcohol, glycerine, or saline solutions 
which withdraw water from the uninjured ascus. On the other hand the expansion 
of the asci (and ejection of the spores) is promoted by placing uninjured asci in water. 
6. The great elasticity of the wall of the ascus is sufficiently shown by the facts 
above enumerated. * 
c. The spores are in many cases retained according to Zopf in the expanding 
apex of the ascus by a special apparatus of attachment'. In Sordaria Brefeldii a 
hollow cylindrical thick-walled process of the membrane, which turns blue with 
iodine, reaches from the apex into the lumen of the ascus. The spores, like those 
shown in Fig. 52, are provided with terminal appendages which connect them 
together in a row; the distal appendage of the uppermost spore attaches the 
entire row to the process from the wall of the ascus, ‘sometimes by thrusting itself 
into its cavity which it fills up, sometimes by closely grasping it. And this apparatus 
is further completed by another arrangement; the membrane of the ascus over a 
subterminal zone is capable of great swelling and can lay firm hold on the appendage 
borne by the chain of spores, as a hand grasps the throat.’ Similar apparatus may 
perhaps frequently be in use especially in the Pyrenomycetes, as is indicated by 
the structural features in the apices of asci which will be discussed in section XXVI. 
Our present knowledge does not allow us to speak with certainty on this point. 
In many cases, especially in the Discomycetes, there is no such apparatus present, 
the spores being suspended in the fluid of the ascus. The spores must have nearly 
the same specific gravity as the fluid; if not, they would change their position as 
the ascus changes its inclination, which they do not do. Most, if not all, spores 
produced in asci sink in pure water; the fluid contents of the ascus must therefore 
be of greater specific gravity than pure water, since it holds in suspension bodies 
of greater specific gravity than water. If increase in the amount of the fluid 
contents causes the apical portion of the ascus to stretch more than the other parts, 
currents must be set up in the fluid in the direction of the apex and continue as 
long as the expansion continues, and push the spores therefore permanently towards the 
apex. The arrangement of the spores may then be affected by special directions 
in the currents which we cannot at present determine, as well as by the conditions 
of space noticed above. 
d. The ascus lined with a layer of protoplasm and preparing to eject its spores 
is in the condition of a cell in a state of constantly increasing turgescence, the 
characteristics of which may here be presumed to be known?. It is natural therefore 
to suppose that the increase in the amount of fluid contents is caused by absorption 
of water by endosmosis, and that this absorption is due to the operation of osmotically 
active substances, dissolved in the cell-contents, which cannot pass through the layer 
of protoplasm. All the facts that have been observed agree with this supposition, 
and especially the circumstance that volume and turgescence can be alternately 
diminished and restored in individual asci by careful removal of water by means 
of a saccharine solution or of glycerine, and by its reintroduction. The opposite view 
expressed in the first edition of this work was founded on the fact that the proto- 
plasmic utricle in the asci which were examined was either injured or killed 
in the process of withdrawing the water, and it has been shown that isolated asci 
are very liable to suffer in this way. The presence of the substances which are active 
agents in inducing endosmosis is evidently coincident with the disappearance of the 

1 As cited on p. 85. 
” Pfeffer, Pflanzenphysiologie, I, p. 50.—De Vries, Mechan. Ursachen d. Zellstreckung, Leipzig, 
1877. 
