ON THE MORPHOLOGY OP HEMILEIA VASTATRIX. 7 



germinal tube, and, like that, generally preserves its uniform 

 calibre throughout. In some cases the similarity between myce- 

 lium and germinal tube is rendered more striking from the contents 

 of the former being also coloured orange- red; as a rule, 

 however, the protoplasm of the internal mycelium is colourless. 

 Vacuoles, granules, and oily drops occur commonly in fresh 

 preparations (fig. 27), but in some cases the branch is filled 

 with a dense, homogeneous protoplasm, shining with a grey, 

 pearly lustre (fig. 26). The "coral-like^' habit of the tufted, short- 

 branched form is well seen in figs. 25 'and 28. 



The Iiaustorium is a somewhat remarkable structure. It con- 

 sists of a stiff, long neck, piercing the cell wall vertically from 

 a branch of the mycelium (figs. 25, 29, 30) ; the distal end is 

 expanded into an ovoid or pyriform body, suspended free in the 

 cell cavity, and containing usually one or two brilliant granules 

 surrounded by a cloudy matrix. In older specimens a distinct 

 wall is evident. Spreading in all directions from the point of 

 entry, the mycelial branches become applied to the exterior of 

 the cells, and feed upon their contents by means of these haus- 

 toria, until a stage is reached when the well-nourished vegetative 

 structure commences to form the spores, wdiich appear externally 

 as "rust.''- 



This process is begun by a tuft of branches collecting in a 

 lacuna, and growing towards the orifice of the stoma, close 

 to which their apices remain in contact for a short time ; the 

 tightly-packed bundle then forces itself into the orifice, and 

 pushes the common apex through to the exterior (figs. 32 and 

 33), where the spores are formed by budding. 



The first spores arise as follows : — The spore-bearing branches, 

 ormed as above described, are filled with fine-grained grey proto- 

 plasm (fig. 33), and on reaching the exterior the apex of each ex- 

 pands into an ovoid sac (PI. Ill, fig. 34), in which the protoplasm 

 accumulates. A succession of other similar sacs arise by bud- 

 ding from the parts below this, and thus a tuft of young spores 

 is formed (fig. 35 and fig. 40 a, b, c). Each of these spores arises 

 by the protrusion of an ovoid sac, remaining narrow below, and 

 becoming constricted off at the neck, where a septum also is 

 formed separating the young spore from the spore-bearing 

 branch (fig. 40). A small pedicel or stalk is usually formed, 

 but the spore is readily detached from this, and it is rarely seen 

 on adult specimens, though the circular place of attachment may 

 frequently be detected. 



Each spore consists at first of a simple, smooth, thin-walled 

 sac, filled with fine-grained protoplasm, in which a nucleus-like 

 body may be frequently observed (fig. 40, c and e). At a very 

 early stage the existence of an endospore can be proved^ but 



