OMPHALIA FLAVIDA 409 



the somewhat depressed upper side of the head (i) are sHghtly 

 separated from one another by the mucilage of their outer walls (j), 

 and they do not bear aerial hyphae but remain naked. 



The flesh of the whole head is solid ; for the space between the 

 pseudoparenchymatous cells, the radiating hyphae, the clavate cells, 

 etc., is filled with transparent mucilage which, doubtless, just as in 

 the thallus of a Fucus, is derived from swollen outer cell-walls. 

 When a head on its stalk is placed in water, no air-bubbles can be 

 seen between any of the cells of the head. The only air-bubble to 

 be observed is a large one which fills the cavity around the end of the 

 stalk within the apophysis. The whole head, owing to its solidity 

 and yellow colour, has a waxy appearance v/hen seen in bright light 



Fig. 205. — The structure and orientation of the gemmifers of Otnphalia flavida. 

 A, a group of four mature gemmifers on the upper side of a leaf-spot of a leaf of 

 Nerium Oleander. During their development, these gemmifers diverged from 

 one another and took up the positions here shown. Each gemmifer consists 

 of : (1) a pedicel which tapers upwards and exhibits a divergence-curvature 

 below its middle point ; and (2) a terminal gemma. The gemma of the gem- 

 mifer farthest to the left has just been blown away from its pedicel by the wind 

 in the direction shown by the arrow. Magnification, 5. 



B, a median -longitudinal section of a single gemmifer attached to an Oleander 

 leaf, shown in its natural position : a, part of the leaf ; b, the pedicel, bearing 

 hairs at its surface ; c, the gemma, produced peripherally into infection hyphae. 

 The pedicel b exhibits two curvatures : (1) a divergence-curvature at d, and 

 (2) a double or sigmoid geotropic curvature terminally at e. The sigmoid 

 bending of the terminal part of the pedicel resulted in the end of the pedicel 

 being torn away from the flesh of the gemma. The gemma is now attached to 

 the pedicel merely by its basal collar or apophysis 'and, in this condition, it is 

 ready for dislodgment and transportation by the wind. Magnification, 38. 



C, the upper part of the gemmifer in B greatly enlarged, to show the histo- 

 logical structure. In this vertical median-longitudinal section the parts may 

 be distinguished as follows : a, the pedicel, with a thicker-walled cortex and 

 a thinner-walled looser medulla (cf. D) ; the terminal part of the pedicel is 

 sigmoidally curved ; the downward curvature b was made in response to a 

 positive geotropic stimulus, and the upward curvature c in response to a negative 

 geotropic stimulus and, when the sigmoid curvature was being formed, the 

 pedicel broke away from the flesh of the gemma to which it previously had been 

 attached at d ; e, a large air-space between the terminal part of the pedicel and 

 the apophysis (collar) of the gemma ; //, the apophysis of the gemma which 

 holds the gemma on to the pedicel until the wind blows it away ; g g, fimbriate 

 cells which form the outer layer of cells of the apophysis ; h, the apex of the 

 gemma, somewhat depressed ; i i, clavate cells separated by a gelatinous 

 matrix y_;' derived from swollen cell-walls ; h k, more swollen clavate cells at the 

 periphery of the gemma, which are produced terminally into aerial infection 

 hyphae II ; mm, pseudoparenchymatous cells embedded in a gelatinous matrix 

 and forming the core of the flesh of the gemma ; n n, slender branched septate 

 hyphae forming the cortex of the flesh of the gemma. Magnification, 405. 



D, a transverse section of the pedicel a little below a in C ; n, the thicker- 

 walled cortex ; b, the thinner-walled medulla ; c c, two hairs. Magnification, 410. 



E, a surface view of part of the apex of the gemma, as seen at h in C : 

 a, clavate cells ; b, the gelatinous matrix formed of swollen cell-walls. Mag- 

 nification, 405. 



Drawn by A. H. R. Buller and Ruth Macrae. 



