88 DIVISION 1. 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. 



b. 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 1 . 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 2 . 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 selution 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. 



3 Pfeffer, Pflanzenphysiologie, I, p. 50. De Vrie?, Mechan. Uisachen d. Zellstreckung, Leipzig. 

 '877- 



