IO 



In the second object under experimentation, oats, besides the direct infection of the ger- 

 minating seedlings by spraying with conidia, a second form of infection was obtained by the 

 introduction of abundant conidia of the oat smut into good compost earth, rich in humus, and 

 also into well manured earth, leaving them undisturbed for some time. The young seed and 

 oat grains were then covered with the soil thus infected and the cultures were left undisturbed 

 in a place not too warm. The sprouting oat grains had to grow through this infected earth 

 layer and, as shown by the experiments, underwent an infection leading to 30 to 40% of smut- 

 ted plants, harvested later. With these experiments it was proved that the germs of infection 

 living in the soil and particularly in manured earth, where they developed further, can attack 

 the host plants and produce smut diseases as found in nature in fields of oats. 



With both experimental plants, Indian millet and oats, the young germinating seedlings 

 are susceptible to infection by smut fungi ; in the third experimental plant, maize, infected with 

 the common smut, the infection experiments on young seed were without result ; only here and 

 there did a young maize plant become smutted or destroyed by a smut swelling. All the other 

 infected plants remained perfectly healthy. They developed into large blossoming maize plants 

 without a trace of disease. Particularly in the pistillate flower spikes of the mature plants, 

 the smut phenomena never occurred. Accordingly, the so universally extensive and striking 

 phenomena of this common boil smut in corn can not be called forth by infection of the ger- 

 minating seedling of the young seed, as was proved in oats and Indian millet. The parts in which 

 infection takes place are to be found in mature plants and could be found without difficulty in the 

 infection material, the conidia of the corn smut, which was acquired in unlimited abundance and 

 easily used. All parts of the mature plant were proved to be capable of infection, if the young 

 tissue of their new shoots grows sufficiently freely and near the outside. Infection could be 

 obtained by injection of bud conidia into the vegetative tip of the young plant as well as in young 

 leaves, young axillary parts and in the young staminate inflorescences, in forms almost never 

 observed in nature. Quite independent of these places, the embryonic cells of adventitious roots 

 and particularly young pistillate flower spikes, appearing ultimately, are proved to be especially 

 capable of being infected. The adventitious roots were transformed into thick smut swellings. 

 The separate ovaries of the pistillate flower spikes were similarly developed into giant smut 

 boils which under certain circumstances caused the whole infected spike to grow to the size 

 of a child's head 1 . It was shown in further experimental infections that only the very youngest 

 tissues are accessible for infection germs and that the parasite remains strongly localized on the 

 point at which it penetrated into the tissue. After an interval of 14 days, the formation of smut 

 spores occurs at this point in the tissue excrescences already formed. The same places in a some- 

 what more advanced condition, the tissues being already hardened, are no longer accessible for 

 action of the fungus. It penetrates them indeed but develops neither tissue excrescences nor smut 

 boils. Susceptiblity of maize to the germs of infection is found in all sufficiently young embryonic 

 parts of the tissue, which are accessible from without. 



(1) Compare the illustrations on plates III-V in Vol. XI. 



