CHAPTER III. SPORES OF FUNGI. 87 



it is the apical and most extensible portion of the wall and chiefly the area forming the 

 lid in that portion which is most distinctly coloured blue with iodine. In the 

 Sordarieae also I frequently saw the ascus open by a comparatively tall lid. 



There is a third series of cases in which the spores are ejected through an apical 

 perfectly circular hole which before ejection of the spores is a circumscribed thinner or 

 less compact portion of the wall of the ascus. In Rhytisma acerinum this hole is 

 replaced by a minute mucro forming the uppermost extremity of the apex of the still 

 closed ascus. In Peziza Sclerotiorum (Fig. 43), P. tuberosa, and their allies, the wall of 

 the ripe but not turgescent ascus is more than twice as thick at the slightly convex 

 apex before the spores are discharged than it is on the sides; it is also formed of 

 two layers and is traversed in the middle by a longitudinal 

 streak which is less strongly refringent and looks like a 

 stopper inserted in the ascus. The apex of the turgescent 

 ascus, ready for the ejection of its spores, is considerably 

 broader and strongly convex outwards, with its wall not 

 thicker than the lateral walls and with none of the in- 

 ternal structure just described. The spores are discharged 

 through the stopper, and after the discharge there is an 

 open passage in its place round which the form and 

 structure of the non-turgescent state are once more 

 restored. In these cases again the apical portion of the 

 wall, which is most capable of stretching and is thickened 

 when it is not in a state of tension, is that which turns 

 blue with dilute solution of iodine, and the stopper which 

 indicates the point of dehiscence is most intensely 

 coloured. 



The following remarks will further illustrate the above 

 short account of the mechanism for the ejection of the 

 spores. 



a. The expansion of the ascus by increase in the amount 

 of its fluid contents has been directly observed. That 

 this is merely a passive stretching of the cell wall, and 

 not a phenomenon of growth with permanent results, is 

 shown by facts which are easily observed, namely, that 

 the ascus contracts to its previous dimensions after dis- 

 charging its spores, or if an artificial opening is made in its wall while its membrane 

 at the -same time increases in thickness, as is shown most clearly in the case of 

 the strong local thickenings which have been described as occurring in Peziza 

 Sclerotiorum. This species shows with peculiar distinctness that it is the apical 

 region of the ascus which stretches most ; but in all other cases attentive comparison 

 will show that it is the apical region, or pretty well the apical half, which is most 

 altered in form and size while the lower half is little or not at all affected. The 

 directions of greatest extensibility and the shapes produced by them vary much 

 in different species, as appears from a comparison of Figs. 43, 44 and 45. The enormous 

 increase in volume of the asci of Sordaria may perhaps suggest actual growth, 

 especially as they are comparatively rich in protoplasm after the spores are matured ; 

 the point requires further investigation, but it should be noticed that the contraction 

 after the ejection of the spores is in this case also very considerable. 



That it is the increase in the amount of fluid content which causes the expansion 



FlG. 43. Peziza (Sclerotinia) Sclero- 

 tiorum. Asci observed as they lay 

 isolated in water, a a mature ascus 

 before ejection of the spores. * the 

 same after ejection, c another specimen 

 in the same stage of development as a, 

 cut through transversely. Magn. about 

 400 times. 



