NOTES AND ABSTRACTS. 



407 



following summer by zoospores. The sporangia require free water and 23 0 C. 

 to 30 0 C. for germination and host penetration. The fungus is disseminated by 

 wind and probably by other agencies — flowing water, insects, and various animals. 

 The control measures suggested are thorough sanitation, crop rotation, and 

 resistant varieties. — A. B. 



Pine Blister Rust. By G. G. Hedgcock, E. Bethel, and N. R. Hunt (Jour. 

 Ai>r. Res. xiv. No. 10, Sept. 1918, pp. 411-424; 4 plates). — The authors find 

 that the aecial stage of the fungus Cronartium occidentale, which is commonly 

 met with on Ribes spp. and Grossnlaria spp., is passed on the nut pines (pinons), 

 and is given the form name of Peridermium occidentale. 



Cronartium occidentale (n.s.) is widespread throughout the States of Colorado 

 and Arizona. Its commonest host is Ribes aureum, but it occurs occasionally 

 on R. odoratum, R. inebrians, and Grossularia leptantha. It has, however, been 

 successfully inoculated on Ribes americanum, R. coloradense, R. Giraldi, R. 

 malvaceum, R. nigrum, R. glandulosum, R. sanguineum, and Grossularia inermis, 

 G. missouriensis, and G. reclinata X G. hirtella. 



The peridermial stage attacks only the pinons (nut pines) ; though inocula- 

 tions were made on twenty-three other species of pines, they have given negative 

 results. 



Cronartium occidentale differs chiefly from C. ribicola (white pine blister rust) 

 in the aecial stage. — A. B. 



Plant Growth, Effects of Barium and Strontium Compounds on. By J. S. 



McHargoe (U.S.A. Jour. Agr. Res. xvi., No. 7, Feb. 1919, pp. 183-194). — 

 The following conclusions were arrived at : 



Barium compounds, in absence of calcium compounds (CaC0 3 ), are poisonous 

 to plants, but in presence of excess of CaCO s exert a stimulating influence upon 

 plant growth. There is no tendency to replace calcium by barium in plant 

 growth when calcium is omitted. Strontium compounds give larger yields than 

 barium compounds. Strontium carbonate cannot be substituted for calcium 

 carbonate in the growth of plants, though strontium carbonate is less toxic to 

 plants in absence of calcium carbonate than barium carbonate. Barium or 

 strontium are not important plant-foods, though small quantities act as stimu- 

 lants in presence of calcium carbonate, and cause acceleration in growth of plant 

 roots. By increasing the amount of strontium nitrate a corresponding increase 

 in the nitrogen content of wheat was obtained. — A . B. 



Plasmodiophora brassicae, Tissue Invasion by. By L. O. Kunkel (Jour. 

 Agr. Res. xiv. Sept. 1918, No. 12, pp. 543-572 ; 20 plates). — The author finds 

 that cabbage plants of all ages up to one year are susceptible to club-root. The 

 typical club-root is the result of a single primary infection, and this forms a 

 morphological unit. The spread of the disease from points of primary infection 

 is accomplished by plasmodia directly penetrating the cells. The cell divisions 

 in the host plant increase the number of infected cells, but have a small part in 

 distributing the parasite through the tissues. 



Infection by direct penetration may be of four stages : 



1. Primary infection of cortical tissues and penetration to the cambium. 



2. Infection of the cambium in all directions from the original point of 

 penetration. 



3. Passage of plasmodia out from the cambium into the cortex, and in from 

 the cambium towards the xylem. 



4. Infection of the medullary rays. 



Infection of a given cell may be temporary or permanent. If temporary it 

 has no noticeable effect on the cell ; if permanent, it stimulates the cell to 

 abnormal growth and division. The growth stimulus is diffuse — that is, it 

 acts on the non-infected cells as well as on the infected cells. The stimulus 

 seems to travel in advance of the infection, specially in the infection of medullary 

 rays and in the early stages of infection, and the disease stimulates the pro- 

 duction of branch roots and shoots. Diseased shoots are unable to react normally 

 to gravity. The mass of parasitic protoplasm in a given volume of diseased 

 tissue is constant in different clubs, and in the clubs of different plants. The 

 average volume relation between host and parasite is approximately in ratio 

 28 to 72. A unit volume of diseased tissue yields the same quantity of spores. 

 The wilting of diseased plants is due, in part, to hypoplasia of cell differentiation 

 in the xylem of the bundles, and the splitting up of the woody cylinder through 

 infection and growth of the medullary rays. 



A short bibliography is appended. — A. B. 



