72 



RESEARCHES ON FUNGI 



The function of the lower heap of protoplasm will be discussed 

 in the Section which treats of the heliotropism of the sporangiophore. 



A sporangium which is still young and intact (Fig. 27) is covered 

 externally on its upper and outer sides by a thin black convex cell- 

 wall which is continuous with the cell-wall of the top of the sub- 

 sporangial swelUng, while below it is separated from the columella 

 by the wall of the columella, which is a thin, almost colourless, 

 convex septum. The wall of the sporangium is remarkable for three 

 special quaUties : (1) its toughness and persistence as compared 

 with the sporangium- wall of Mucor, which is diffluent ; (2) its intense 



Fig. 29. — Pilobolus Kleinii. Dehiscence of the sporangium. A, a ripe sporangium 

 shortly before dehiscence ; it crowns the top of a subsporangial sweUing s and is 

 covered by a black wall w. B, the sporangium just after dehiscence : a layer 

 of jelly a lining the interior of the lower part and sides of the sporangial wall 

 has swollen and thereby caused the sporangium -wall to break transversely into 

 two parts, an upper cap-like parti) and a basal band c ; d, spores which can be 

 seen through the protruding jelly. C, what is left of B after the sporangium 

 has been stroked away under water with a needle : s, the subsporangial swelling ; 

 e, the columella ; and c, the band of sporangium-wall encircling the base of the 

 columella. Magnification, 66. 



blackness ; and (3) its complete resistance to being wetted by water. 

 As we shall see later, all these quaUties are biologically significant. 



The contents of a sporangium which is still young and intact 

 are two : (1) a mass of several thousand orange-yellow oval spores 

 packed closely together and embedded in a matrix that swells up 

 somewhat when brought into contact with water ; and (2) a sohd 

 transparent mass of jelly which is disposed in the form of a ring 

 around the base of the columella between the sporangium-wall 

 and the spores (Figs. 27 and 30, A). 



The spores are dichroic : when mounted in water under a cover- 

 glass and viewed with the low-power objective of a microscope, 

 they are orange-yellow in transmitted light and greenish in reflected 

 Ught. 



