50 EXPERIMENT STATION RECORD. | Vol. 40 



The white spot disease of alfalfa, P. J. O'Gaba (Science, n. ser.. 1,8 (1918), 

 No. 12S8, pp. 299-301). — While carrying on experiments on the treatment of 

 soils with various water soluble substances, the author observed that white 

 spot of alfalfa appeared in two or three days after treatment of the soil. No 

 injury to the crowns could be found and no parasites were present. White spot 

 of alfalfa did not appear where the concentration of the water soluble sub- 

 stance was below a certain amount. Further experiments are said to have in- 

 dicated that the soil solution alone did not produce white spot but that the 

 coincidence of several environmental factors, as soil temperature, atmospheric 

 temperature, relative humidity, and light, is necessary. 



The investigation is said to have progressed to the point where the author 

 believes that the osmotic pressure of the soil solution is one of the important 

 factors in the production of white spot, not only under experimental condi- 

 tions but under field conditions as well. In the intermountain country where 

 these Investigations were carried on. it was noted that fields showing a con- 

 siderable Incrustation of alkali when irrigated exhibited white spot in more or 

 less amount, depending upon the other environmental factors above mentioned. 

 A sudden rise of tlie water table in Irrigated district- is also said to have brought 

 about the same condition of the plants in the Held. 

 An extended report on these Investigations Is to be published later. 

 Bean diseases in Vermont, II. K. Babtram {Ann. Rpt. Vt. State Hort. Roc, 

 15 (1917). pp. 28-88). — This discussion deals with an insect pest (the bean 

 weevil) and with bean diseases musing serious trouble In Vermont, including 

 pod spet (anthracnose), dry rol (a new but Berious trouble ascribed to a Fusa- 

 rium), the true bean rust, and bean blight (bacterial). 



Important potato foliage diseases, I. K. Minus (IotCO Apr., t8 i 1917), 

 4, pp. 170 /?..').- A brief discussion is given of potato blackleg, curly dwarf, 

 and tipburn. also of appropriate control measurt 



Tissue invasion by Plasmodiophora brassicae, L, < >. Ktwkii. [Jour. .\<ir. 

 R search [U. S.], /.J {1918), No. It, pp*. 50, figs. 2).— In a previous 



publication i B, 8. R'., 33, p. 346), the author described the tissue penetration 

 .of Spongospora Bubterranea on the potato. In the present paper, which is a 

 contribution from the Bureau of riant Industry, U. S. Department of Agri- 

 culture, an ace, mnt is given of a study of clubroot, in which is presented In- 

 formation regarding the nieth.nl of tissue Invasion by P. braartcw. 



The author found that cabbage plants of all ages up to one year are suscep- 

 tible to clubrti.it. provided they are actively growing. The typical club Is a 

 morphological unit, usually the result of a single primary infection, but by the 

 coalescence of several swellings a compound club may be produced. The spread 

 of the disease from points of primary infection is accomplished through direct 

 invasion of cells by Infecting Plasmodia. Host cell divisions increase the number 

 of infected cells, but have a very small part in distributing the parasite through- 

 out the tissues. The Infection of a given cell may be either permanent or 

 temporary, and if permanent it stimulates the cell to abnormal growth and 

 division. The growth stimulus is diffuse and seems to travel in advance of in- 

 fection. The mass of parasitic protoplasm in a given volume of diseased tissue 

 was found to be remarkably constant in different dubs and in the elul.s of differ- 

 ent plants. The average volume relation between hosl and parasite iii the tis- 

 sues studied is approximately given by the ratio 28: 72. 



Asa result of this study, it is claimed that the method by which /'. brassir,r 

 infets host tissues differs from that of 8. tubtt rranea, but if judged by the kind 

 of galls produced and by the position of diseased tissues, it is believed that the 

 method of infection for SorospfuBTQ veronica, Sorodiscut cattitrichi*, and Tetra 

 nu/ju palustn may lie similar to that found for P. brOUicas, 



