146 



RESEARCHES ON FUNGI 



dependent on several different factors of which osmotic pressure is 

 only one, and among which we may recognise (1) the osmotic 

 pressure of the cell-sap, (2) the great elasticity of the cell-wall, (3) the 

 suddenness with which the aperture in the end of the sporangio- 

 phore is formed when the explosion takes place, (4) the control of 



the explosion, in that 

 the wall of the sporan- 

 giophore breaks open 

 not irregularly but at a 

 single prepared place — 

 a circular subterminal 

 line or ring, and (5) the 

 opening at the end 

 of the sporangiophore 

 having a smooth rim 

 and being just of the 

 right size (not too large 

 and not too small) for 

 permitting the cell-sap 

 to be forced through 

 it in sufficient quantity 

 and with a sufficiently 

 high initial velocity 

 to carry off the projec- 

 tile advantageously. It 

 is the combination of 

 all these factors which 

 makes the Pilobolus 

 gun so wonderfully 



Fig 



71. — Pilobolus longipes. Pliotomicrograpli of 

 the upper side of a dischaiged sporangium and 

 of the drop of cell-sap (now dried) which 

 accompanied it ; No. 1, the precipitate of the 

 cell-sap, consisting of both organic and inorganic 

 matter, in part in the form of branched crystals ; 

 No. 2, a broad clear ring-layer of jelly in contact 

 with the glass on which the projectile came to 

 rest ; No. 3, the couve.x, very black, sporangium- 

 wall covering many thousands of spores ; No. 4, 

 a few spores lying under the jelly, they were 

 forced out of the sporangium when this struck 

 the glass. Magnification, 51. 



effective. 



An Analysis of the Cell-sap of Pilobolus longipes.— An inspection 

 of a vertical section through a fruit-body of Pilobolus longipes {cf. 

 Figs. 27 and 28, pp. 69 and 70) suggests that at least nine-tenths of 

 the fruit-body consists of cell-sap. When the sap is in situ in the 

 subsporangial swelling and stipe, it is a very clear fluid. Dissolved 

 within it, however, are various crystalloidal substances ; for, when 

 a few drops of the sap are extracted from a number of fruit-bodies 



