3- Infection. 



became irresistible, that tliis smut exclusively infects the flower, and that it is 

 not developed in the same year but remains latent in the mature grain. When 

 this grain is sown next season, the myceUum passes into the young plant and 

 then, on reaching the inflorescence, proceecb to the formation of smut spores. 

 It is very evident, therefore, that it was the mycelium in the seed which 

 caused the disease, for the grains were sterilized and disinfected before sow- 

 ing, so that every chance of infection from spores adhering to the grain was 

 excluded. Further, to protect them against contamination in the soil, the 

 grains were sown in germinating chambers on a layer of sterilized sand, and 

 when the developing grains had reached the immune stage, the plants were 

 carefully laid out and grown in the op3n. 



The methods adopted by Brefeld in carrying out experiments to prove 

 that infection took place through the flower, are of sufficient interest to 

 justify mention of them, and they wera such as approached most nearly the 

 natural infection. The most favorable time was when the flowers were 

 most fully opened and the spores were powdery and easily scattered, condi- 

 tions met with in dry sunny weather. As the result of various preliminary 

 trials, Brefeld found that a hollow India-rubber ball was the best for apply- 

 ing the spores, an apparatus similar to that used for applying " Mortein," 

 only the ball was larger. The smutted inflorescence was introduced into the 

 ball and a tube inserted in the opening, so that the smut spores could be 

 forcibly blown out in the form of a fine spra3^ The ears to be infected were 

 placed in a glass cylinder, closed below by cotton wool, and the spores were 

 blown in from above. After a short interval to allow the spores to settle, 

 the ears were removed from the cylinder and thus infection of the flowers 

 alone was made the subject of the experiment. 



Of course only a limited number of flowers open at the same time to allow 

 access to the spores, for it is well-known that they do not op^sn all at once, but 

 generally those in the middle of the ear are most advanced, while those at the 

 top and bottom are later. Hence with only one infection a vertain proportion 

 are always missed, and there is no advantage in infecting the same ear at 

 different times, since the necessary handling hinders the normal development. 

 When infection tak.:!s place in the field, the chances are proportionately in- 

 creased, for the spores are being constantly scattered upon adjoining healthy 

 plants with the slightest breath of wind, and it is only interfered with by 

 rain or damp weather. Warm and dry weather is also unfavorable for the 

 germination of the spores, while it hastens the ripening of the grain. 



A second and more delicate method consisted in the artificial infection of 

 each flower, just as in cross-fertilization, using a fine cameFs hair brush to 

 dust t e spores on the stigma of the flower. 



This is more reliable than the " cylinder-infection," since all flowers not 

 infected may be removed, but it must not be assumed that each flower left 

 is actually infected, for all the flowers of an ear are not capable of infection at 

 the same time. By either of these methods, flower infection experiments 

 were carried out on wheat and barley, and while the grains produced seemed 

 Cjuite healthy and normal, yet on being sown the following year under strict 

 sterilization conditions, smutted ears appeared at harvest time in greater 

 or less proportion. Although Brefeld succeeded in inoculating the wheat- 

 flower, for instance, and observed a few days afterwards that the spores had 

 germinated in the stigmatic secretion and had sent hyphae through the stig- 

 matic tissues to the ovary, yet it must not be assumed that this is the only way 

 in which flower infection takes place in nature. It is well-known that the 

 flower of wheat is self-fertilized before opening, so that the smut spores will 

 in all probability, fall upon the young ovary wall when exposed and thereby 

 gain an entrance. 



