1896.J Vegetable Physiology. 139 



ficially, a few of the spores being transferred to a fresh nutrient solu- 

 tion every four days. The first trial (500 seedlings) was with conidia 

 which had been cultivated in this manner for six months. These seed- 

 lings yielded from 7 to 10 per cent of smutty plants. The second trial 

 was with conidia which had been cultivated for a year. This experi- 

 ment was almost wholly negative, 300 of the seedlings yielded no 

 smutty plants and 200 more gave only 1 per cent. The explanation 

 was not far to seek since at the end of this period the conidia had 

 almost wholly lost the ability to send out germtubes and along with it 

 the power to infect the plants. Microscopic examination showed that 

 the germtubes can penetrate into any part of the young seedling but 

 this does not necessarily mean infection. The latter takes place only 

 when the smut hyphse are able to reach that part of the plant where the 

 smut beds form. In all of these experiments the smut germs penetrated 

 the young seedlings but the smut beds appeared only in the floral 

 organs, some months intervening between the entrance of the fungus 

 and the appearance of the smut in a totally different part of the plant. 

 Those germtubes which enter the plant and fail to reach the incipient 

 ovaries become enclosed in the mature tissues of the host plant and are 

 incapable of further growth and this frequently occurs even in young 

 seedlings. 



The infections obtained with the big sorghum plant are even 

 more interesting. Nearly all of the first series of infections were 

 destroyed by a hail storm, but of the 32 plants which escaped 12 be- 

 came smutty. The seedlings of the second series were infected indoor 

 in March and set out the first of May. The plants grew luxuriantly 

 and by the middle of August had reached a height of 5 to 7 feet. The 

 first smutty panicle appeared August 16 and for some time thereafter 

 it appeared as if all of the plants would be smutty, the infected panicles 

 developing first. Finally sound ones began to appear. In the end 

 there were 158 smutty plants out of 274. A third series of experiments 

 was instituted to determine in what stage of germination the sorghum 

 plant is most susceptible : 252 seedlings sprayed in the earliest stage of 

 germination, gave 180 smutty plants. " The development of the smut 

 in the earliest and strongest plants, which reached a height of 8 feet, 

 was striking. The big panicles were attacked in toto and projected out 

 of the luxuriant green foliage like black brooms." There can be no 

 doubt that infection stimulates the growth of the plant. Older seed- 

 lings yielded less striking results : 150 which were infected when the 

 embryo was a centimeter long, gave only 24 smutty plants ; 1 90 infected 

 when the embryo was 1* cm. long gave 12 smutty panicles; 221 infec- 



