GENERAL SUMMARY 463 



hand, never puff but liberate their spores in a steady stream which may- 

 continue for hours, days, or weeks. 



Not only large Discomycetes but also small ones puff, so that puffing 

 is not correlated with fruit-body size. 



Puffing was first described by Micheli in 1729 and has been noticed 

 by all mycologists since his time. In 1916, Falck divided the Discomy- 

 cetes into : (1) the radiosensitive which emit spores when warmed by 

 radiant heat given out by a lamp or the sun, and (2) the tactiosensitive 

 which puff when touched or blown upon. In 1926, Ziegenspeck came to 

 the conclusion that the opening of the asci at the moment of puffing is 

 not due to a stimulus but is a purely mechanical phenomenon caused by 

 a slight additional strain in the ascus walls at their apices. 



Photographs, made by Dickson and Fisher, illustrating the spore- 

 clouds of Sclerotinia sclerotiorum given off at the moment of puffing have 

 been reproduced. 



Conceivably, the asci of a Peziza might discharge their contents one 

 by one in the order of ripening. Why then does a Peziza puff ? Falck 

 has supposed that the dependence of Morchella, Gyromitra, Verpa, etc., 

 on a sufficiently high temperature for the discharge of their spores caiises 

 spore-discharge to be delayed until the heat of the sun brings into ex- 

 istence air-currents which may assist in spore-dispersal ; and he also holds 

 that the dependence of many Pezizaceae on the wind for the discharge 

 of their spores causes spore-discharge to be delayed until the wind is 

 sufficiently strong to be effective in carrying away the spores. In these 

 ecological theories there may well be some truth. It was in the hope of 

 throwing more light on the phenomenon of puffing that an investigation 

 on Sarcoscypha protracta was undertaken. 



Sarcoscypha protracta occurs in young Poplar bush {Populus tremu- 

 loides) in the suburbs of Winnipeg, and its fruit- bodies appear near the end 

 of April and at the beginning of May. The cups are scarlet in colour 

 and conical in form, and they look upwards toward the sky. They are 

 attached to buried roots by a pseudorhiza ; and the pseudorhiza, like 

 that of Collyhia fusipes, is perennial. 



When a fruit-body of Sarcoscypha protracta puffs, the spores are shot 

 straight outwards from the conical hymenium in directions which are 

 parallel to the cup's longitudinal axis. The distance to which the spore- 

 cloud was shot before dispersing irregularly was found in three fruit- bodies 

 to be 8 cm., 12 cm., and 17 cm. (= 7 inches) respectively. 



Each ascus opens obliquely and the opening faces the mouth of the 

 cup and consequently the sky. On this account, although the asci are 

 straight and are obliquely inclined toward the long axis of the cup, the 

 spores are shot not from one side of the cup to the other, but straight 

 upwards through the mouth of the cup and parallel to the cup's long 

 axis. 



Owing to the contraction of the cell-wall, an ascus, when discharging 



