4i8 RESEARCHES ON FUNGI 



means, e.g. wind, rain-splashes, etc., from one place to another. 

 (4) The exterior layer of each gemma is mucilaginous, so that a 

 gemma readily adheres to the upper surface of a leaf on which it may 

 happen to fall.^ (5) The pear-shaped palisade cells all around the 

 outer side of the oblate-spheroidal part of each gemma bear more or 

 less radiately-directed filiform hyphae — the infection hyphae. When 

 a gemma falls on a leaf, these filiform hyphae grow over the surface 

 of the leaf (Fig. 212, H), pierce the cuticle, pass through the epidermis, 

 and soon invade the palisade cells and spongy mesophyll.^ In less 

 than a week, the mycelium in the leaf -spot begins to form new 

 gemmifers (Fig. 213, A and B, p. 424). 



The Basal Curvature of the Pedicel and its Significance.— 

 When a gemmifer growing on the upper side of a leaf or a malt-agar 

 plate is very young, the pedicel projects outwards perpendicularly 

 or almost perpendicularly from its substratum and the gemma is 

 always situated symmetrically on the end of the pedicel (Fig. 212, 

 A and B). As the pedicel increases in length by intercalary growth 

 just beneath the gemma, its lower or basal half usually becomes 

 curved, so that the upper half of the pedicel and the gemma are 

 turned away from the perpendicular at an angle which often varies 

 from 30° to 45° (c/. Fig. 212, C, D, E. ). 



At first it was thought that the basal curvature of the pedicel 

 just described might be due to the stimulus of gravity, but experi- 

 ment soon disproved this supposition. Gemmifers were grown on 

 malt-agar : (1) in upright Petri dishes, (2) in inverted Petri dishes, 

 (3) in vertically placed Petri dishes, and (4) in Petri dishes rotated 

 in a vertical plane on a klinostat. Under all these conditions the 

 gemmifers at first grew out perpendicularly from their substratum, 

 and then their pedicels became more or less curved in various 

 directions {cf. Figs. 202, p. 403, and 213, p. 424). In the inverted 

 and vertical Petri dishes, the pedicels did not all curve 

 downwards as they should have done had they responded to' a 



1 F. G. Kohl, " Untersuchungen liber die von Stilbella flavida hervorgerufene 

 Kaffeekrankheit mit Angaben der aus den Untersuchungen sich ergebenen Mass- 

 regeki gegen diese Pilzepidemie," Beihefte zum Tropenpflanzer, Bd. IV, 1903, 



pp. 63-64. 



2 Kohl shows the infection hyphae growing from a gemma into a leaf in his 



Taf. 11, Fig. 7. 



