13 



BLOSSOM INFECTION BY SMUT FUNGI. 



For our experiments in determining blossom infection in the host plants of smut fungi, 

 those forms come first and chiefly under consideration whose spores are powdery and whose 

 spore masses are easily scattered by the wind and thus distributed. These are, first of all, the 

 different forms of loose smuts which occur in our grains, — the loose smut of barley, of wheat and 

 of oats. The characteristically chosen name, loose smut (Flugbrand), indicates the distribution 

 of the spores by wind, in nature. 



The spores of the loose smut, however, are not the only ones which may be considered 

 for blossom infection. We have seen in maize smut that the spores themselves of the spore 

 masses were not scattered, but that, in the germination of spores on a saprophytic soil substratum, 

 air conidia are formed which in the place of smut spores take over the distribution of the germs 

 of infection. And the results of infection experiments with maize smut have furnished the most 

 conclusive proof that these air conidia are at least just as effective for the infection of the host 

 plants. 



Aside from maize smut there are still other forms of smut fungi which develop just as 

 diffusible air conidia, in which we must consider the possibility as to whether they too can reach 

 the blossoming plants by means of the air. These are, for example, Ustilago destruens'^, and 

 especially the stinking smut of wheat: — forms of Tilletia. In all the cases here named, plants 

 are involved ivhose pollen is disseminated by wind and also at the same time forms of smut fungi 

 with similar dissemination. 



Smut fungi occur, however, also in the blossoms of host plants, fertilized by insects, whose 

 smut spores are not disseminated like the loose smut. An especially striking case of this kind is 

 the anther smut of the plants fertilized by insects. On these host plants, only the anthers are 

 transformed into the spore masses and the spores from these anthers do not have the powdery 

 nature of the loose smut. The smut spores are disseminated very little, if at all, by the air, but 

 are held fast in the anthers, and are first forced out of these by the insects which visit the blos- 

 som. The fact can escape no attentive observer that the anther smut in white or light colored 

 blossoms ; for instance, M elandryum album and Saponaria officinalis, is betrayed by a peculiar 

 blemishing of the blossom head by violet smut spores. External proof is here given that insects, 

 visiting the blossoms, force out the anther smut as well as the pollen. They carry over the 

 spores of the smut as well as pollen to the stigmae of the blossoms, where conditions for their 

 germination and further development are to be found in the stigma secretion itself. 



We will place the forms of loose smut most prominently because investigation has advanced 

 furthest here and the results arrived at are as forceful as they are convincing. 



Formerly only one form of loose smut was differentiated, which was called Ustilago 

 carbo and which was thought to live in oats, wheat and barley as host plants. In the middle of 



(1) See figs. 9-12, plate VI, Part V of this work. 



(2) See illustrations on plates XII and XIII, Part V of this work. 



