BOTANY. 317 



on Phalaris arundinacea, (c) agrostidis on Agrostis vulgaris and A. stolo- 

 nifera, (d) agropyri on Triticum ripens, and (e) hold on Holcus lanatus 

 and H. mollis. 



(8) Species undescribed. — Forms (a) epigasi on Galamagrostis epigeios 

 and (&) melicce on Melica nutans. 



In addition studies not yet completed have shown that besides the 

 black rust of the 23 grasses given, the rusts found on the following 

 species of grasses have been found to be true forms of black rust: 

 Airafiexuosa, Alopecurus nigricans, Elymus glaucifolius, Panicum milia- 

 ceum, Phleum boelimeri, P. michelii, Poa chaixii, P. pratensis, and 

 Tritic urn unicu m . 



Spreading of rust is often insignificant (1) between small grains and 

 grasses that may carry the same specialized fungus forms; (2) from 

 and to the plant species carrying winter rust in case such form is 

 found; and (3) occasionally between different cultural forms of the 

 same grain species. 



The viability of summer and winter rust spores is in many cases 

 small or at least uncertain. 



The spreading of the rust depends to a large extent on the distance. 

 In a circular recently issued by the Swedish Agricultural Department 

 it is ordered that no barberry, whether wild or planted, be allowed to 

 grow at a distance less than 25 to 50 meters (82 to 164 ft.) from grain 

 fields. 



The viability of the winter spores is dependent on certain exterior 

 conditions (moisture, temperature, etc.) and is limited to a short time. 



The yellow rust appears on certain particularly susceptible kinds 

 of wheat and barley 4 to 5 weeks after sowing 



The intensity of the yellow rust has sometimes proved greater on 

 open than on shaded parts of the same field. 



Shoots of wheat which early in the spring were enclosed in wide 

 glass tubes closed at both ends with cotton, developed stalks which 

 were rusty after C to 8 weeks. In the same way barley plants of a 

 kind easily attacked by yellow rust, grown in sterilized soil and pro- 

 tected against contagion from without during the entire growing 

 period, have in certain cases after G to 8 weeks become infected with 

 yellow rust. 



The fungus lives for a long time a latent life in the cells of the germ, 

 and shortly before the appearance of rust spots, in the presence of 

 favorable outer conditions changes to a visible mycelium. 



The general conclusion is therefore drawn that the appearance of 

 the grain-rust disease depends primarily upon a disease germ present 

 in the plant itself, which in certain cases is inherited from the mother 

 plant in the seed grain and lives there, as well as in the plant grown 

 from the seed, a latent life as '< mycoplasma;" and, secondarily, on 

 infection from without from diseased neighbors. The intensity of the 

 disease depends (1) on the energy with which prevailing external con- 



