45 



the development of air conidia. On this account it is advisable to sterilize impure seed of 

 maize in order to destroy thereby all smut spores clinging to its surface. 



If we take into consideration the fact that air conidia of the maize smut lead to infec- 

 tion of the mature host plant and that they alone may bring it about, that these air conidia, 

 driven by the wind into the openings and rifts of the host plants, attack the young tissues to 

 be found there and make them smutted, it then becomes self-evident that maize plants which, by 

 enveloping leaves, shut ofif all young tissues, susceptible to attack externally, must be at the same 

 time the most resistant to this smut. These are the large varieties, to which belong especially 

 the horse-tooth maize. It must be just as self-evident that the usually smaller varieties of maize, 

 in which the leaves open over the vegetative point like a paper sack and in which the pistillate 

 flower spikes are less protected by their husk leaves, show a marked susceptibility to the smut. 

 The experiments described above and reported in Part XI of this work\ were made accident- 

 ally with a smaller variety of maize which is especially suitable for experimental infection. Only 

 later compafative experiments with other maize varieties showed clearly how these are protected 

 by the above named accessory conditions from the blowing in of the germs of infection and 

 how it must naturally ap])ear that in this variety the smut is formed only rarely. 



(1) Plates III-V. 



