TILLETIA TRITICI 233 



This rudiment is at first globular (Figs. 108, p. 222, and 110, C, 

 p. 225), but soon it develops more on one side than on the other, 

 so that it grows upwards from the axis of the sterigma at an angle 

 of about 45°. As growth continues, the conidium becomes curved 

 and, when fully grown, it is sickle-shaped (Fig. 114, A-D, s). The 

 time taken for a conidium to grow from a tiny rudiment to full size 

 is from an hour and fifteen minutes to an hour and a half. 



During the growth and maturation of a secondary conidium 

 developed on an H -shaped pair of primary conidia, the cytoplasm 

 and the two nuclei which these contain are gradually transferred 

 to the secondary conidium, so that in the end the H -shaped pair 

 of primary conidia becomes emptied of its contents. As emptying 

 proceeds, the two primary conidia become septate, the septa being 

 produced in succession and serving to cut off those parts of the 

 conidia which have become free from protoplasm (Fig. 114, A). 

 The process of septation in the promycelium is of a similar nature 

 and will be described in detail in a Section called The Phenomenon of 

 Protoplasmic Migration. 



During the growth and maturation of a secondary conidium 

 developed on a mycelium (Fig. 114, B), a mass of protoplasm is 

 transferred from the mycelium via the sterigma to the conidium. 

 The hypha concerned thus gradually loses its contents and, like the 

 H -shaped pair of secondary conidia just described, becomes septate. 



As soon as a secondary conidium has attained maturity (Fig. 114, 

 D, a), a tiny drop of liquid begins to be excreted from the spore 



Fig. 114 — cont. 



has produced sterigmata st which bear secondary conidia (secondary basidio- 

 spores) s. The protoplasm migrated out of the pair of primary conidia and out 

 of the mycelium, except at a, c, and below the immature conidium b, and, 

 during the migration, the primary conidia and the mycelium became septate. 

 The secondary conidia (secondary basidiospores) s s are shot from their sterig- 

 mata by the drop-excretion method illustrated in D. Magnification, 660. 



C : a diagrammatic representation of a mycelial mat at the surface of malt- 

 agar. Part of the mycelium sm is submerged and somewhat knotty, while the 

 rest of the mycelium m is aerial. The aerial part of the mycelium bears sterig- 

 mata and secondary conidia (secondary basidiospores) s s which in general are 

 directed away from the substratum. Magnification, about 330. 



D : stages in the discharge of a secondary conidium (primary or secondary 

 basidiospore) of the kind shown in A, B, and C : a, a full-grown conidium 

 (basidiospore) on its sterigma ; b, about two seconds later, a drop of liquid has 

 just been excreted from the spore-hilum ; c, about 18 seconds after b, the drop 

 has now attained its maximum size ; d, about one second after c, the spore 

 and the drop have been violently shot away from the sterigma. Magnification, 

 767. 



