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RESEARCHES ON FUNGI 



pyriform. For mechanical reasons connected with the resistance 

 of the air, when the spore, after becoming pyriform, is falling, its 

 rounded end is directed downwards and its pointed end upwards ; 

 so that, finally, it settles in the manner shown in Figs. 126 and 127. 

 One question, however, still remains to be answered : Why, when 

 drying, does the spore buckle up, so that its two arms become closely 

 applied one against the other ? The drop excreted from the spore- 

 hilum just before spore-discharge undoubtedly travels with the 

 spore, as in the Hymenomycetes 1 and the Uredineae. 2 In all 

 probability, in Tilletia tritici, as may actually be seen in abnormal 



Fig. 127. — Semi-diagrammatic lateral view of part of a spore-deposit of 

 secondary basidiospores of Tilletia tritici, collected in dry air. The 

 spores fell from an inverted agar plate, (c/. Fig. 128) through the dry 

 air of the laboratory on to a glass slide (for a surface view of the spore- 

 deposit vide Fig. 126). The plate was raised only about 1 cm. above 

 the slide. The air of the laboratory was very dry. a and b, two 

 views of one spore ; c and d, two views of a second spore ; e and /, 

 two views of a third spore. Whilst falling through the air, the first 

 and second spores completely doubled up and the third spore became 

 much bent. Magnification, 1330. 



excretion (cf. Fig. 118, c and e, p. 243), the drop makes its way into 

 the hollow on the concave side of the spore, i.e., on the side which 

 looks upwards as the spore is falling. It may be imagined that, in 

 some way, as the drop is drying up, by means of its adhesive and 

 cohesive properties, it pulls the two halves of the spore together so 

 that, finally, they come to touch one another and to adhere together. 

 It may be remarked that the wall of a basidiospore of Tilletia tritici 

 is extremely thin, so that it can offer but little resistance to any force 

 exerted upon it by the drying drop. 



If to such a fresh dry spore-deposit as that shown in Fig. 126 one 

 adds a drop of water, the majority of the spores at once spring open, 

 re-assume their sickle-shaped form, and fall over on their sides so 



1 A. H. R. Buller, Researches on Fungi, Vol. II, 1922, pp. 5-18. 



2 Ibid., Vol. Ill, 1924, p. 504. 



