104 Loose Smut of Oats. 



the one with protoplasmic contents puts forth a germ-tube, or it may swell 

 out at the end and form another conidium. Thus fusion of the conidia 

 occurs where a number of them are aggregated together, and even more than 

 two may in this way be united. 



This is the typical mode of development, the spore producin.g a germinal 

 tube or promycelium, from which conidia are budded off, but there ara various 

 departures from this. Under certain circumstances, according to Kuehn, the 

 promycelium may not develop conidia, but becomes an ordinary hypha and 

 penetrates the tissues of the host-plant by its pointed extremity. Again, 

 various fusions may take place by means of a tube from one segment to an- 

 other of the same promycelium, or the promycelia from different spores may 

 unite in a variety of ways by means of branches. Thus, the upper segment 

 may become connected with the lower segment of the same promycelium by 

 means of a curved tube, or two succeeding segments may become united by 

 w^hat Brefeld calls a buckle-joint or knee-joint. This is very common with 

 spores germinated in both water and nutritive solutions, and consists of the 

 unequal growth of one side of the promycelium at the level of a septum. As 

 this protuberance grows the promycelium itself becomes bent at an angle. 



So far the behaviour of spores in water has been shown, but when placed 

 in a nutritive solution, such as hay infusion, there is a difference, as Brefeld 

 has pointed out. In the first place, they germinate cjuicker, as might be 

 anticipated, and the promycelia and conidia are larger. Then the various 

 fusions do not occur, but the most important difference is that the detached 

 conidia multiply themselves by budding after the manner of yeast and form 

 what are known as sprouting conidia. By keeping up a supply of the nutrient 

 fluid, Brefeld maintained this process of budding for more than a year, and, 

 ■whenever this was exhausted, the budding ceased. The sprouting conidia 

 retain their vitality for about two months if kept moist, but when allowed to 

 dry there was no perraination after the sixth week. It becomes a question 

 of greal practical interest how long the various reproductive bodies retain their 

 germin ting power and under different conditions of moisture. While the 

 sprouting conidia only retained this power for about six weeks when kept 

 dry, Brefeld found that the spores germinated as freely at the end of two 

 years as when fresh. Another observer. Von Liebenberg^ germinated the 

 spores at the end of seven and a-half years, so that the time limit of germina- 

 tion may exceed that considerably. 



Infection. 



Infection by this smut has been specially studied by Brefeld,^ and a 

 description of it will give a clear idea as to how^ this happens in smuts of this 

 type. The spores are produced exclusively in the spikelets. It had already 

 been shown by Wolffs and Kuehn ^ that infection takes place only in the 

 seedlin ; stage, and Brefeld followed the mycelium in the growing plant until 

 it reached the ovary of the flower and formed its spores. 



He brought about infection not directly with the spores, but with pure 

 cultures of the " yeast-spores," or sprouting conidia, derived from the budding 

 conidia grown in a nutritive solution. The young seedlings specially grown 

 were sprayed by means of an atomizer, with the " yeast-spores " mixed up in 

 water, and after a short time were planted out. Accordin ' to the stage of 

 growth at which the seedlings were infected, there was a definite percentage 

 affected with the disease. In the earliest stage of the seedling, while still in 

 the bud, 17 to 20 per cent, were diseased ; when about 1 cm. long, there were 

 7 to 10 per cent, diseased ; when 2 cm. long, and still enclosed in the sheathing 

 leaf, there were only 2 per cent, diseased ; while in older seedlings there was 



