/r Fungi of Illinois. 145 



the common red cedar, constituting the so-called "cedar balls," 

 of orange color, especially noticeable after a rain in the month 

 of May. The relation of these two forms of the fungus was 

 not suspected until carefully established by Oersted, a botanist 

 giving special attention to such matters, and well qualified for 

 such observations and experiments. The fact having been as- 

 certained, a thoroughly practical remedy consists in clearing 

 away the worthless red cedars, or, in case of a few of these 

 trees, which for any reason are wished to be saved, picking off 

 and burning the u cedar balls." In this case the spores pro- 

 duced on the apple leaves cannot germinate and grow on the 

 apple, but must reach, by wind currents or otherwise, the cedar 

 leaves ; where alone one essential stage of development takes 

 place. From the cedar the spores must again be carried to the 

 apple tree, or allied host, thus alternating back and forth as a 

 necessary requirement of continued existence. 



This is by no means a solitary example of known alterna- 

 tions which render possible the agency of man in preventing 

 plant diseases caused by these pernicious parasites: but to gain 

 the fullest possible mastery we still need much investigation 

 and experiment by those most competent to conduct them. It 

 has long been known that the rust of wheat (Pnccinia grami- 

 nis) has an alternate form on the barberry bush, but since the 

 rust occurs in vast regions of our country where no barberry 

 exists, we know that this plant is not positively essential to the 

 continuous development of the rust. It now seems probable 

 that the barberry stage is a reality, and perhaps in some way 

 beneficial to the Puccinia (rust), but not essential. It still re- 

 mains, however, to be ascertained whether or not there is some 

 other common plant usually found in or near the wheat fields, 

 which takes the place of the barberry, and thus permits the 

 continued growth of the rust. 



What might be the practical value of investigation in this 

 direction? There are annually produced in Illinois about 50,- 

 000,000 bushels of wheat. The destruction of one-hundredth 

 part of the crop by this fungus probably falls, as an estimate, 

 far within the actual limits of loss as an annual average. This 

 represents 500,000 bushels, which, at seventy-five cents per 

 bushel, is 1375,000. If it could be demonstrated that' the eradi- 



