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 moisl 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. confluens. and Rhytisma acerinum, in 

 addition to the species which have been already named. Many other observations 

 haw been recorded since the time of Micheli. 



In Ascobolus and the genera which haw been recently separated off from it 

 ejection is never successive btit always simultaneous from all the asci that are at any 

 time ripe in the hymenium, and here too wc 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. 



