51 



FINAL CONSIDERATION. 



From the preceding experiments as a whole, it is obvious that the previous assumption 

 of a successful infection of smut fungi limited only to germinating seedlings is not universally 

 satisfactory. Besides infection of the young seedlings still other forms of infection exist which 

 had been overlooked. 



W c can report in general that only the youngest embryonic 'tissues of the host plants are 

 the ones attacked by the germs of infection. The germs of the smut fungi have no power of 

 attacking older parts of plants the tissues of which have become hardened. 



Experiments on the infection of maize smut proved clearly that the large host plants, in 

 the case of their development and formation, expose in different places the youngest embryonic 

 tissue to the attack of infection germs of maize smut. These points of attack extend even to 

 the embryonic pistillate inflorescences which usually appear only after the complete maturing of 

 tlie plants. In maize the young leaves of the vegetative tip, the staminate inflorescences and the 

 young axes may be reached by germs of infection, blown upon them. In the same way also 

 infection of the pistillate inflorescences and adventitious roots takes place in the host plants. 

 That infection has taken place is easily and surely determined here and the appearance of smut 

 occurs after the lapse of perhaps three weeks. The smut remains localized upon the separate 

 places in which inoculation was successful and occurs independently on all the above-named 

 places which are susceptil)le to smut germs and capable of infection by them. 



In the other smut forms occurring in our grain the matter is essentially different. The 

 phenomena of disease do not develop in the parts in which infection has taken place. The 

 effect of the infection is shown only after a long period of incubation, after many months, with 

 the unfolding of the inflorescences. In the inflorescences alone are provided the only places for 

 the formation of spore masses and these inflorescences lie at the opposite end of the host plant 

 from the one attacked in the first stages of the germination by the germs of the fungi. The 

 host plants during their whole life are surrounded externally by mature and hardened tissues, 

 into which the germs arc not al)le to penetrate. The host plants only once and indeed only at 

 the beginning of their develo|)ment offer external young tissue to the germs of infection. These 

 are the first germinating stages of the young seed in which infection must take place in the soil, 

 if smutted plants are to be produced subsequently. These facts correspond throughout to the 

 previous and older theory that infection of smut fungi takes place in the young seed. This 

 undoubtedly happens, Init in thus judging it, the fact was overlooked that host plants, at the time 

 of flowering, offer again in their ovules and stigma?, very young and assailable tissue for the 

 germs of infection and that infection can take place in the embryonic parts of the pistillate inflor- 

 escences as well as in the young germinating seedlings in the soil. 



Thus our investigations have produced certain proof, that this infection actually takes 

 Ijlace in the lilossonis and that, carried by wind or insects, the smut dust is brought from smut- 

 ted individuals to healthy plants. 



