90 DIVISION I.—GENERAL MORPHOLOGY. 
atmosphere. If the hymenium is only moderately damp, so that the tips of the ripe 
projecting asci look like a slight rime or a fine down on it, the puffing commences 
in a few seconds after the bell-glass or other covering is removed. If it has been 
kept very wet, the hymenium is covered with a thin layer of water and glistens more or 
less and is of a darker colour than in the moderately moist condition. In such a 
hymenium the puffing does not take place till the layer of water is evaporated and 
the slight rime-like appearance is observed ; the puffing is accelerated by whatever 
accelerates the evaporation. 
From these facts it appears that sudden loss of water is the proximate cause of 
the puffing. Since puffing occurs instantaneously in hymenia that are not wet, the 
withdrawal of water as soon as dry air comes in contact with the Fungus cannot 
produce it by causing a shrinking and contraction of the entire hymenium and a 
consequent increase of the pressure on the asci from without. All this could not 
possibly be brought about to any important extent in one or a few seconds of time, 
and some simple experiments and measurements are sufficient to convince us that the 
pressure which operates on the asci from without under long-continued desiccation is not 
at first increased, and eventually decreases to a considerable extent, but that it increases 
in proportion as the hymenium absorbs water. 
The loss of water can only therefore cause the puffing by altering the state of 
tension in each ascus, either by lessening the expansion of the lateral walls and so 
increasing the pressure of the fluid contents on the place of dehiscence, or by lessening 
the power of the place of dehiscence to resist the pressure which remains unaltered. 
The correctness of this explanation is confirmed by the observation, that ejection takes 
place when ripe isolated asci lying in a little water are suddenly exposed to the 
operation of reagents like alcohol and glycerine which withdraw their water. 
The above remarks leave little room for doubt that motion and shaking affect 
the puffing only by hastening the evaporation of the water. A hymenium which 
has just sent forth a cloud of spores can be induced to repeat the operation several 
times, if the plant is moved rapidly to and fro, and the less perfectly ripe asci are 
made to dehisce. But then, and in many cases after the first puffing, a rest of at least 
some hours is necessary, that a sufficient number of new asci may come to maturity 
to allow the puffing to be observed. 
The phenomenon of puffing is absent from some Discomycetes; I have never 
been able to excite it in Peziza pitya, Morchella esculenta, or Exoascus Pruni; it is 
readily produced in the majority of species. I have observed it in Peziza melaena, 
P. tuberosa, P. aurantia, P. cupularis, P. badia, P. confiuens, and Rhytisma acerinum, in 
addition to the species which have been already named. Many other observations 
have been recorded since the time of Micheli. 
In Ascobolus and the genera which have been recently separated off from it 
ejection is never successive but always simultaneous from all the asci that are at any 
time ripe in the hymenium, and here too we have the phenomenon of puffing. The 
mechanism of the discharge and the conditions for the puffing are the same as those 
which have been described in the case of the other Discomycetes ; but they are also 
dependent on the illumination to an extent which requires to be more closely 
examined. 
