1 1 



.Icfordiinily. in the Am/,- maize plant, the matter is quite different from that in oats and 

 Indian millet. This plant offers the fungi germs, in the different life stages of its vegetative points, 

 young tissue accessible from without, for example, in its embryonic leaf buds, young axes, in the 

 ailvi-mitiou> roots suppU'inenturily formed, the pistillate flower spikes etc. In oats and Indian 

 millet these tis-ues are shut off from the outside and are inaccessible for the germs of infection. 

 For this reason, the young maize plant is not attacked by the germs of infection in the young 

 >ee<l hut in the mature plant. The parasite which has already penetrated into the tissue remains 

 strongly localized in the place penetrated and every part accessible to infection, in the young 

 leaves, blossoms, axes and roots, must be infected by itself if the smut boil is to be produced 

 which at the latest appears after three weeks. 



The etiology of the common smut accordingly differs essentially from that of the two 

 earlier cases and the manner in which infection is carried out in nature is not less different. Smut 

 spores which did not germinate in water, produce bud conidia in saprophytic substrata, in rich, 

 mouldy and well manured earth quite the same as in the translucent nutrient solutions. These bud 

 cotiidia very soon pass over into air conidia and it is the air conidia* which easily disseminated 

 through the air reach, without any difficulty, the susceptible parts of the host plant in which we 

 observe the appearance of smut. Further, it is conidia produced by saprophytic nutrition, and 

 especially air conidia, which carry out infection in nature. Entire maize plants grown for 

 experimental infection became smutted without exception if the infection was properly carried 

 out. 



The experiments, as far as given in Part XII of this work, ended with these results. 

 Experimental infection was repeated in later years in order to obtain smut material, also, for the 

 purpose of instruction and produced thereby a number of additional results. 



It was discovered, in experiments on maize smut, that the susceptibility of the host plant 

 is not limited to one part of the young germinating seedling as had been previously supposed, but 

 re-occurred in the most various parts of the matured plant, and that the young blossoms of the 

 pistillate spikes are particularly susceptible to infection from without. This discovery leads of 

 itself to the closely related consideration, whether this case of blossom infection, as proved for 

 maize smut, might exist only in maize. Evidently it is the young tissues of the pistillate blos- 

 soms and of the ovules which in maize can be directly attacked. In unbiased, comparative judg- 

 ment, nothing stands in the way of the assumption that in other host plants inhabited by smut 

 fungi, the ovaries with pistil and stigma, should also be accessible for infection. They too consist 

 indeed of young tissues which may be attacked freely in the open air by infection germs as are 

 the ovaries of the pistillate flower spikes of maize. If no possible cleistogamy exists in the blos- 

 soms they are accessible for the germs of infection from without so far as disseminated by 

 the air. Without doubt, a second place of infection exists here which had entirely esca|>ed 

 observation and had to remain so, as long as the etiology of the common smut in maize was not 

 known. For this reason it was possible for the previous conception, according to which the 

 young germinating seedlings alone could be infected by smut germs, and also that mature plants 



(1) See figs. 1-9 plate II. Part XI. 



