THE PILOBOLUS GUN AND ITS PROJECTILE 145 



Osmotic Pressure of Leaves as determined by Dixon and Atkins 



Species and Dates 



Aloe americana,* Jan. 11 

 Saccharum officinale * Dec. 10 

 Monstera deliciosa* Dec. 10 . 

 Anthiiriuin andreanum,* Jan 



27 . 

 Platyceriuni alcicorne,* Jan. 2 

 Wistaria sinensis, Sept. 30 

 Anthurium crystallinum* J an 



27 . 

 Vitis Veitchii, Oct. 2 

 Heliantlius multiflorus, Oct. 2 

 Equisetum tdmateia, lateral 



branch, Aug. 14 

 Musa sapietdum* Dec. 10 

 Equisetumtelmateia, main stem 



Aug. 14 . 

 Agave americana * Jan. 11 

 Selaginella mertensii,* leaves 



and aerial stems, Jan. 27 

 Poll/podium iriodes* Jan. 27 

 Eucalyptus globulus, Nov. 29 

 Cordyline australis, Nov. 28 

 Passiflora quadrangular is, Dec 



10 



Species and Dates 



Ilex aquifolium, new, ultimate, 



Dec. 4 

 Uhmis campestris, Oct. 2 

 Fraxinus oxyphylla, Oct. 3 

 Ilex aquifolium, antepenult! 



mate, Dec. 4 . . 



Pinus laricio, leaves one year 



old, Nov. 30 

 Apium graveolens (etiolated 



bases), Dec. 5 

 Populus alba, spring leaves 



Aug. 28 . . , 



Chamaerops humilis, mature 



Nov. 28 . 

 Hedera Helix, Nov. 29 . 

 Populus alba, summer leaves 



Aug. 28 , 

 Magnolia acuminata, Sept. 30 

 Cerasus laurocerasus, Nov. 28 

 Chamaerops humilis, just ex 



panded, Nov. 29 

 Fraxinus excelsior, Sept. 30 

 Syringa vulgaris, Aug. 13 

 Syringa vulgaris, Aug. 22 



O.P. 



14-65 



14-88 

 15-06 



15-14 



15-50 



15-66 



15-95 



1713 

 17-29 



17-88 

 18-07 

 18-31 



19-22 

 19-52 

 24.10 

 25-50 



Growing in greenhouses. 



By reference to the Table it will be seen that in only one species, 

 namely, Aloe americana, was the leaf sap found to have an osmotic 

 pressure less than 5-5, i.e. less than that of Pilobolus. It is there- 

 fore evident that the osmotic pressure of the cell-sap of Pilobolus, 

 relatively to the osmotic pressure of the cell-sap of the leaves of most 

 of the higher plants, is low. 



Factors in the Efficient Working of the Pilobolus Gun.— It may 

 be asked : how is it that the Pilobolus gun, notwithstanding that 

 its cell-sap has a relatively low osmotic (turgor) pressure, can shoot 

 its projectile to a maximum measured height of six feet and a 

 maximum measured horizontal distance of eight and a half feet ? 

 The answer is : firstly, an osmotic pressure of 5 - 5 atmospheres is, 

 after all, a strong pressure, for it is equal to about 82 lbs. to the 

 square inch ; and, secondly, the action of the Pilobolus gun is 



VOL. VI. 



