Methods in Rust Investigations 253 



sign of a uredinium shows, all other plants are removed leaving the 

 one plant with the one uredinium under the lantern globe. From this the 

 culture is multiplied. 



Another method, more easily used, consists in lightly dusting some 

 spores on a pot of plants grown under a lantern globe. When uredinia 

 first show, but before they have broken the epidermis, a plant is selected 

 showing only one uredinium, all the rest being eliminated. If no such 

 plant is found, but a plant is found having only one uredinium on a 

 leaf, all the leaves but that one are cut off. By such a method one 

 is not quite so certain of having a pure line as in the former, but in 

 many cases it is practically as good. 



11. Cultures of Rust Free from Other Fungi. In the usual culture 

 work with rusts it is not necessary to exclude other fungi, especially 

 saprophytes, yet if investigations looking toward the growing of these 

 parasites on artificial media are undertaken, the rusts must be free from 

 saprophytic fungi which otherwise will rapidly overgrow the cultures. 

 The writer (1917) has elsewhere described such a method. 



To recapitulate briefly, urediniospores of Puccinia Sorgld are sown 

 on the upper side of leaves of corn plants grown in large sterile test 

 tubes, from seed disinfected with cori'osive sublimate. The first uredinia 

 occur on the lower side of the leaves, and spores from these are sown 

 on similar test-tube cultures of corn plants. Thus the rust might be 

 said to have been strained through the corn leaf. Another method is to 

 float small pieces of leaves from sterile corn plants on sterile sugar solu- 

 tion in small capsules. These pieces of leaves will take up the sugar 

 solution and live for a considerable period. Spores taken from a freshly 

 opened uredinium are used to inoculate the pieces of leaves in a num- 

 ber of these capsules. Spores from uredinia developed in those capsules 

 which do not show saprophytic fungi are then used to inoculate a fur- 

 ther series. 



12. Recording Data. When only a few individuals of a small num- 

 ber of species or varieties are being studied, it is relatively easy to 

 record in detail the symptoms produced when infected with rust. If an 

 attempt is made to describe in detail all the symptoms shown by a large 

 number of varieties, the time necessary for such notes becomes a serious 

 limiting factor. To meet this difficulty a system of symbols has been in 

 use in this laboratory, thus reducing the time necessary for note taking. 

 These symbols indicate the terms applicable to the symptoms. They are 

 as follows: 



i = immune, no signs of infection. 



f ^ flecks. 



k =: killed or necrotic areas. 



M = mottled or chlorotic areas. 



s = susceptible, no signs of resistance. 



c = uredinia in concentric circles. 



g = green islands of tissue surrounded by chlorotic. 



The size of the uredinia is denoted as follows: 

 m = minute. 



