GENERAL SUMMARY 471 



sphaeroidal part of the gemma is covered with aerial radiating filaments 

 which the author has called infection hyphae. It is these hyphae which 

 enter and infect a new host-leaf when a gemma has fallen upon it. 



A sporophore of Omphalia flavida is a much larger structure than a 

 gemmifer, for it is 0-6-1 -5 cm. in height and its pileus is 1 •5-2-5 mm. in 

 diameter. It liberates an abundance of spores which readily germinate 

 in .malt-agar. Freshly-fallen spores were introduced into a wound in a 

 Bryophyllum leaf, but no infection resulted. From the observations of 

 others, it appears that the infection of Coffee leaves in Coffee plantations 

 is due to gemmae and not to basidiospores. 



A comparison of the external form and the internal structure of a 

 gemmifer and of a sporophore of Omphalia flavida justifies the conclusion 

 that a gemmifer is a highly specialised sporophore in which the pedicel 

 is homologous with a stipe and the gemma homologous with a pileus. 

 In a gemmifer the pileus has ceased to develop lamellae and basidia 

 and has become detachable at maturity and thus converted into an 

 organ of dissemination. 



A pedicel of a gemmifer of Omphalia flavida is at first quite straight 

 but, as it grows in length, it becomes bent at a little distance above its 

 base through an angle of 30°-45°. This basal curvature is not due to 

 gravity. When a number of gemmifers are growing together in a culture, 

 the pedicels by means of basal curvatures come to diverge from one 

 another. It thus appears that the pedicels of gemmifers mutually repel 

 one another. 



The abscission of a gemma of Omphalia flavida from the end of its 

 pedicel in preparation for the detachment of the gemma from the pedicel 

 by the wind takes place whilst the apophysis of the gemma firmly clasps 

 the pedicel subterminally, and it is effected by the end of the stipe be- 

 coming sigmoidally curved and so withdrawing itself from the gemma. 

 The sigmoid curvature of the end of the pedicel is alv/ays made in a vertical 

 plane and, as experiments with a Pfeflfer klinostat have shown, is due 

 to a positive and a negative reaction to the stimulus of gravity. 



A ripe gemma of Omphalia flavida which has undergone abscission 

 from the extreme end of its pedicel and is holding on to the pedicel merely 

 by means of its clasping apophysis is readily detached from its pedicel 

 by the wind. When a gemma falls on to a leaf of a host-plant, it usually 

 settles so that it rests on its sHghtly concave upper surface. Under 

 moist conditions its jDeripheral infection hyphae then resume their growth 

 and may penetrate into the leaf's interior tissues. 



Detached gemmae of Omphalia flavida retain their vitality for over 

 24 hours under moist conditions but, when exposed to dry air, they soon 

 die. 



Wounded and unwounded leaves of Bryophyllum calycinum and un- 

 wounded isolated leaves of Nerium Oleander and of a species of Ficus, 

 after having been inoculated with gemmae of Omphalia flavida, developed 



