DISEASES OF PLANTS. 759 



tion is called to the relation which exists between the freezing point of plant juices 

 and the average molecular weights of the substances contained by them. On 

 account of the varying composition of the plant juices during different periods of 

 germination the freezing point also varies. 



Kansas weeds, A. S. Hitchcock andG. L. Clothier (Kansas Sta. Bui. 66, pp. 54, 

 pj 8- 77) _ — A. catalogue briefly describing 209 species of weeds occurring in Kansas, 

 and giving illustrations of their fruits and seeds. 



DISEASES OF PLANTS. 



New investigations concerning the specialization, propagation, 

 and origin of the black rust, J. Eriksson (K. Landt. AJcad. Handl. 

 TidsJcr., 35 (1896), pp. 182-198). — The following- summary indicates the 

 scope of this paper and the status of knowledge of this subject: 



The black rust (Puccinia graminis) is found in a number of different 

 specialized forms, characterized not only by their summer and winter 

 spore stage on the grasses, but also by their aecidium stage on the bar- 

 berry and Mahonia. Three different forms are found on cereals: Rye 

 rust (f. sp. secalis), common on rye and barley and also appearing on 

 Triticum repens, T. caninum, Bromus secalinus, and Elymus arenarius; 

 oat rust (f. sp. avenm); oat rust, also appearing on Dactylis glomerata, 

 Alopecurus pratensis, Avena elatior, Milium effusum, and other .masses; 

 and wheat rust (f. sp. tritici), so far found in nature only on wheat. The 

 rye and oat rusts are sharply confined to their respective species of 

 grasses, and there is little danger of their occurring on other kinds of 

 plants. Under certain conditions the wheat rust differs from the other 

 grain rusts in that it may be propagated both in its summer spore and 

 aecidium stages on closely related grains, at least on rye and barley. 

 The rusts of Aira, Poa, and Agrostis are, so far as now known, wholly 

 harmless to the cereals. 



Barberry and Mahonia, being bearers of many of the biologically 

 different seeidium forms, of which one corresponds to the rye and barley 

 rust, another to the oat rust, etc., a rusty barberry (or Mahonia) can 

 only infect grains to which its particular rust belongs, if the barberry 

 (or Mahonia) infected with wheat rust be excepted, which can infect 

 not ouly wheat, but also other cereals, at least rye and barley. By 

 observing the grasses growing in close proximity to a barberry during 

 the preceding fall and winter, one can judge as to its possible harmful- 

 ness and determine whether or not it ought to be removed to protect 

 the grain to be grown near it. The propagation of the black rust from 

 rusty grasses to barberry, as well as from barberry to the grasses, may, 

 at least during dry seasons, be disturbed and even prevented, either by 

 a comparatively narrow intervening strip of tree growth (100 meters), or 

 by very small (10 to 25 meters) open spaces. At a distance of 25 meters 

 from a barberry bush the black rust is found to the same extent in all 

 directions. Some differences may be observed according to the luxu- 

 riance of the different plants, the most luxurious plants tirst becoming- 

 rusty. 



13777 — ]So. 8 5 



