22 



out of the smut spores, with the young germinating seedlings was direct and extensive. In the 

 third case tlie dry seed was covered with infected compost. In the fourth case, with compost which 

 had been mixed with one-half its volume of sterilized fresh horse manure. In the last two cases 

 the effect of the manured compost must have made itself felt. In order to judge correctly the 

 effect of these forms of infection of the germinating seedlings by means of spores of the loose 

 smut in wheat, we must investigate first of all the germination of the smut spores in water 

 and in nutrient solution. The material kept from the previous year, through the whole winter, 

 weakens somewhat in germinating strength and germinates only very slowly. In spore material 

 which is not preserved with special care no germination whatever occurs'. The germination of 

 the smut spores of the loose smut in wheat is not fructificative^. No conidia are formed, but 

 only germinating tubes which sprout from the cells of the hemibasidia. No increase of the 

 germs of infection therefore occurs here, not even when nutrient solutions are used. Because 

 of this the strength of the infection of young germinating seedlings by smut spores is more 

 restricted in the soil than in other smut forms which germinate fructificatively. In compost and 

 manured earth this made itself especially felt, since here infection can result only through the 

 germinating tubes of the hemibasidia in direct contact with the grain. The chances left for a 

 successful infection of the germinating seedlings, according to the condition of spore germination 

 of the material gathered the previous summer, are from the very beginning, so far as summer 

 wheat is concerned, strongly decreased and improbable. It is scarcely possible to understand 

 how smut spores from the preceding vegetative year, which had germinated weakly in the spring 

 or not at all, can bring about infection of the germinating seedling. 



In fact all the experimental infection tried with summer wheat resulted negatively. From 

 all the plants inoculated as young germinating seedlings there developed only entirely healthy indi- 

 viduals free from smut. The infection of the young germinating seedlings remained therefore 

 unsuccessful even in most varied and numerous experiments, as may be seen from the following 

 survey printed in small type. It should not be assumed that more favorable conditions for 

 infection can exist in nature than were created and used in our experiments. We are there- 

 fore justified in drawing the conclusion that the infection of the young germinating seedlings is 

 little or only slightly probable in nature. We consider our experiments in this line as not yet 

 completed. We will continue them in the next few years and will consider further any possible 

 contingencies. 



The experiments in the forms given were attempted also in autumn with smut material 

 gathered about four months earlier, in which the germinating strength of the spores had 

 decreased but little. It was just as impossible to produce any smutted plants by this infection. 

 Therefore in the loose smut of wheat we face the fact that blossom infection is fully and 

 indeed totally successful and that infection of the germinating seedlings is restdtless. We must 

 conclude from this that, in this loose smut, blossom infection is the ruling form of infection, if 

 not the only one. 



(1) Compare the results of the investigation on germination already given in Part XII. 

 <2) Compare the illustrations on plate VII, Part XII. 



