72 Sfi///;/itg Smut or Bunt in Wheat. 



2. But if the spore germinates in water and the promycelium at length 

 reaches the air, conidia are formed which become detached and are free to be 

 distributed by the wind. 



3. If the detached and paired conidia happen to germinate in moist air, 

 they invariably produce secondary conidia, which are minute and easily de- 

 tached, and may readily be carried by the slightest breath of air to a distance. 



4. If these secondary conidia reach a place sufficiently moist, they produce 

 a germ-tube for the infection of the wheat-plant, but if there is not sufficient 

 moisture, they give off another conidium at one side, and so on until even- 

 tually they may either produce a filament which will enter a wheat-plant or 

 die of exhaustion. 



5. If nutriment is added to the water in the shape of organic matter, each 

 primary and secondary conidium is capable of producing filaments which 

 ultimately form a mass, like a tuft of mould, visible to the naked eye. The 

 aerial branches develop sickle-shaped conidia, which are easily detached and 

 readily distributed, and again give rise to a tufted mycelium bearing conidia, 

 and so on. This shows how the conidia may be preserved in an active con- 

 dition where organic matter is present. If there is sufficient moisture the 

 conidia will germinate, and instead of perishing, if there is no wheat-plant at 

 hand into which they may enter, they will absorb nourishment and grow 

 like a mould and produce secondary conidia, which may, in their turn, either 

 germinate or remain dormant according to the amount of moisture. 



It is interesting to note that while Ustilago only produces spores in the 

 host-plant, Brefeld succeeded in producing spore-like bodies with Tilletia in 

 artificial cultures. Under these conditions the conidia give rise to hyphte, 

 which, after growth in length has ceased, begin to thicken in a moniliform 

 manner, and then transverse septa are formed which isolate the roimded cells. 

 After becoming free, they grow no more, but concentrate their contents 

 and thicken their membrane, gradually assuming a dark colour and net-like 

 markings on the walls. Although so far developed, they did not germinate 

 when placed in suitable solutions. 



There are thus two stages in the life history of this smut to be clearly dis- 

 tinguished — the 'parasitic stage, starting from the period of infection up to 

 the time when spores are produced, together with conidia and secondary coni- 

 dia, and the sapropJiyfic stage, commencing with the germination of the coni- 

 dia in a nutrient solution and producing conidia in damp air which are capable 

 of infection. 



Although the conidia arising from the promycelium and those produced 

 from the mould-like mycelium are distinct in their mode of origin and in their 

 shape, yet they have much in common. The former arise as a whorl at the 

 apex of the promycelium and are generally elongated and filiform, while the 

 latter are always formed singly from a hypha, and are shorter, thicker, and 

 sickle-shaped. But in a nutrient solution, Brefeld has shown that both coni- 

 dia form a mycelium, and when a number of cultures are made in water, those 

 produced by the hyphee assume all sorts of transition shapes, from the elon- 

 gated filiform to the typically sickle-shaped. 



Duration op Germinating Power. 



The spores produced in the ovary retain their power of germination for 

 two or three years at least, and Liebenberg^ states that he has germinated 

 them after eight-and-a-half years, of course after being kept under dry con- 

 ditions. Since these dry conditions do not exist under ordinary cultivation 

 for au entire season, it may safely be assumed that if a change of crop after 



