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 inthe amount rıc.43. Peetea (Sclerotinia) Sclero- 
. = > tiorum. Asci observed as they lay 
of its fluid contents has been directly observed. That zen in water a@ a mature scan 
this is merely a passive stretching of the cell wall, and before ejection of the spores. 6 the 
A R same after ejection. c another specimen 
not a phenomenon of growth with permanent results, is in the same stage of development as 2, 
shown by facts which are easily observed, namely, that St meug» wansversely. Magn. about 
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 
