I24 RESEARCHES ON FUNGI 



is constantly increasing in volume, and it may be readily supposed 

 that this mass-increase of protoplasm must cause protoplasmic 

 movement toward the growing points. As Reinhardt 1 showed 

 forty years ago, a mycelial hypha elongates only at its very tip ; and 

 yet, as may be easily observed, a growing hypha, even when elongat- 

 ing very rapidly, has its end full of protoplasm (cf. Figs. 62, C, and 

 63, E, pp. 114 and 116). It is not to be supposed that the 

 protoplasm which fills the end of a rapidly growing hypha is all 

 manufactured at the hypha's tip. Rather we must suppose that 

 the terminal cells of the hypha, surrounded as they are by an 

 unexhausted nutrient medium, are manufacturing new protoplasm 

 throughout their length and that, in consequence, there is a steady, 

 although slow and scarcely perceptible, movement of the protoplasm 

 toward the growing point, which results in the growing end of the 

 hypha being kept full of protoplasm. In rapidly growing hyphae 

 of Pyronema confluens, Gelasinospora tetrasperma, and Rhizoctonia 

 solani, I have succeeded in observing the gradual pressing forward 

 of the protoplasm past the last, just-formed septum, from the 

 penultimate into the terminal cell, and toward the apical growing 

 point ; and, furthermore, in a species of Ciboria and in Rhizoctonia 

 solani, as will be described more fully later on, I have observed that 

 the last-formed septum (sometimes several of the last-formed septa) 

 of a growing hypha becomes temporarily bulged forward toward the 

 apical growing point as the somewhat viscous protoplasm presses 

 against it, flows through its pore, and passes toward the end of the 

 hypha (Fig. 82, p. 163). 



In a mycelium which has exhausted its culture medium and which 

 is forming fruit-bodies or producing hyphae that are growing in a 

 film of water or in moist air, the cause of the rapid flow of protoplasm 

 from the older hyphae which have ceased to grow into the newer 

 hyphae which are elongating and branching vigorously is vacuolar 

 pressure. In a young mycelium which is growing in a fresh culture 

 medium and in which the vacuoles are still very small, the slow flow 

 of protoplasm toward the apical growing points must be due to 

 pressure arising from the general increase in volume of the proto- 



1 M. 0. Reinhardt, " Das Wachsthum der Pilzhyphen," Jahrb. f. wiss. Bot., Bd. 

 XXIII, 1892. 



