HISTORY OF PILOBOLUS 25 



deposit was treated with cold water. Only two-thirds of the deposit 

 was dissolved. The percentage composition of the soluble portion 

 of the deposit was found to be : 38-8 organic substances (no carbo- 

 hydrates) ; 20-5 K2O and 'Na.^fi (chiefly K2O) ; 19-3 AUOg and 

 FegOa: 1-5 SO3 ; 14-5 P2O5 ; 4-2 CI; 1-4 CO.^ and, finally, 

 traces of SiO^. Altogether, the sap contained 1-2 per cent, of 

 soluble and 2-9 per cent, of insoluble substances. It was found 

 that the excreted drops contain 0-5 per cent, of mineral salts of the 

 same nature as those contained in the cell-sap, but no organic sub- 

 stances. The drops have an alkaline reaction, as may be determined 

 with Utmus paper, and this reaction is due to KoCOa.^ 



Lepeschkin's statement that the excreted drops are completely 

 devoid of organic substances cannot be accepted ; for, as Knoll ^ 

 subsequently discovered, the drops contain a colloid in consequence 

 of which, as they dry up, their surface assumes an uregularly 

 wrinkled appearance (Fig. 42, C, p. 86). However, it may well 

 be that this colloidal substance is not excreted along with mineral 

 salts from the vacuole of the sporangiophore but, as Knoll beheves, 

 is formed b}^ local mucilaginisation of the cell- wall. ^ {Cf. Fig. 43, 

 p. 87.) 



If the sporangiophores are transferred to dry laboratory air, 

 even although the substratum contains plenty of water, they at 

 once begin to dry, soon become flaccid, and eventually bend and fall. 

 With the diminution of cell-turgor, the energy of excretion becomes 

 smaller and smaller and soon the excretion of drops ceases com- 

 pletely. To revive a flaccid sporangiophore, it is necessary to place 

 it in air which has at least 90 per cent, moisture in it.* 



Tufts of Pilobolus {Pilzrasen) were set on salt solutions which 

 diminish the cell-turgor. In spite of very great air-moisture, a 1 per 



^ W. W. Lepeschkin, " Zur Kenntnis des Mechanismus der aktiven Wasseraus- 

 scheidung der Pflanzen," Beihefte z. Bot. Centralb., Bd. XIX, 1906, p. 421. 



2 F. Knoll, " Untersuchungen iiber den Bau und die Funktion der Cystiden und 

 verw-andter Organe," Jahrb.f. wiss. Bot., Bd. L, 1912, pp. 488-489. 



^ Knoll {loc. cit., pp. 453-500) found that the cystidia of a number of Hymeno- 

 mycetes excrete potassium oxalate which crystallises out in the slime formed from 

 the cell-wall. Whether or not the drops excreted by Pilobolus contain traces of 

 organic substances other than colloidal slime, which Lepeschkin failed to detect, 

 remains to be determined by further analyses. 



* W. W. Lepeschkin, loc. cit., p. 413. 



