i6 Spore-forniation. 



CHAPTER IV. 



Spore-formation in Australian Genera. 



The mode of formation of the spores is often characteristic of different 

 genera, and therefore it becomes necessary to see wherein the difference lies. 

 The much-branched spore-forming hyphaB generally become greatly swollen, 

 and their walls gelatinize. Then the spores arise within the old cells by the 

 formation of a new membrane, and it is in the details of this process that 

 variety occurs. 



Ustilago. 



The development of the spores has been closely followed by Fischer von 

 Waldheim.3 The fertile threads or spore-forming hyphfe become enlarged 

 and excessively branched, and are densely crowded together. Then the gela- 

 tinization of the walls begins, and this proceeds to such an extent that the 

 cavity is almost obliterated at first, only appearing as a narrow shining line 

 in the centre of the hyphse (Plate I., e). Next, a swelling of the surface of the 

 hyphee takes place at certain points, often close to one another, so that they 

 appear nodose, and the cavity at the same time is enlarged. The hyphae 

 continue to increase in size and consequently become intertwined and tangled 

 together, so that eventually they have actually coalesced. The irregularities 

 of the hyphfe become more marked, and it is evident that the spores are begin- 

 ning to be dehnitely formed as the swellings get more and more rounded. The 

 crowded spore-forming hyphse with their numerous branches, as they develop 

 the spores, ru}i together in a complex mass, so that their individuality is almost 

 entirely lost (Plate I., /). They appear as a gelatinous mass studded with 

 numerous shining points in the form of streaky or rounded bodies. The pro- 

 cess of spore-formation, or the commencement of the differentiation of the 

 protoplasmic contents to form a spore, is indicated by the entire mass of the 

 hyphse breaking up into distinct portions, which, however, retain their con- 

 nexion with one another until the spores are completely formed and they are 

 surrounded by a more or less dense gelatinous envelope. The spores become 

 more or less polygonal from mutual pressure, but ultimately separate from 

 each other and assume their typical spherical shape. The differentiated con- 

 tents increase in size and contain fat granules, and a distinct contour is per- 

 ceptible corresponding to the outer spore membrane. The outer edge of this 

 contour darkens, and even while still surrounded by a thin gelatinous envelope, 

 the irregularities of the epispore begin to appear. As the spores ripen the gela- 

 tinous membrane disappears and there is no trace of it at maturity, nor are 

 any remains of the mvcelial hyphae attached to them, although it is often seen 

 in Tilletia (Plate I., Z;). 



Thus in Ustilago, the spore-forming hyphse with their numerous branches 

 are divided up by means of septa into short swollen cells, which become con- 

 verted into spores. These are produced in an irregular manner, so that the 

 entire mass of mvcelium is ultimately transformed into a dark-coloured mass 

 of spores (Plate I., d). 



Melanopsichium. 



In a cross-section of the rachis or axis of the inflorescence attacked by the 

 smut the plant tissue is seen to be excavated by the fungus, leaving a (^,entral 

 core more or less intact, and portions extending towards the epidermis. In these 

 cavities the sori are produced and the spores are first formed at the centre of 

 the sorus and graduallv extend outward all round, so that the younger and 



