986 EXPERIMENT STATION RECORD. 



due to the nematode Heterodera schachtii. The author reports this nematode as 

 attacking oats, winter and spring wheat, barley, rye, maize, and to sonic extent the 

 different rye grasses, timothy, and orchard grass. He \v;is unable ti> recognize it in 

 brome grasses, vetches, peas, horse beans, white mustard, buckwheat, or spurry. 



Various means tor combating nematodes are discussed, and the use of large appli- 

 cations of Chile saltpeter is recommended. 



The secidium of maize rust, .1. ( '. Arthur (lint. Gaz., 38 (1904), No. 1, />/>. 

 64-67). — An account is given of the discovery of the secidial form of the common rust 

 of corn, Puccinia sorghi. The author noticed the common infection of a species of 

 Oxalis and the plants seemed to be in close association with a mass of debris made 

 up largely of broken cornstalks. The affected plants of Oxalis were not found beyond 

 the deposit of cornstalks, and acting upon this hint the author suspended over a 

 potted plant of corn a number of rusted leaves of Oxalis and in a few days the char- 

 acteristic appearance of the maize rust was produced. It is therefore considered that 

 the secidium of P. sorghi occurs on Oxalis, and a verification with teleutosporic 

 material will be undertaken. 



The author notes a few references to literature giving an account of the occurrence 

 of fecidia on Oxalis and he thinks there is little doubt but that in every case it is to 

 be associated with the maize rust. 



The water relation of Puccinia asparagi, R. E. Smith (Bot. Gaz., 38 (1904), No. 

 1, pj). 19-43, figs. 21). — The author presents an elaboration of certain features of inves- 

 tigations on the asparagus rust previously noted (E. S. R., 16, p. 66), giving a detailed 

 discussion of the water relation of the fungus causing the disease. He summarizes 

 his investigations, showing that there is a direct relation between the effect of 

 moisture and the germination and development of spores and mycelium of the rust. 

 This relation is of greatest importance when absolute conditions for control prevail. 

 Dew is an absolute necessity in infection by rust and is more important in the devel- 

 opment of the parasite than rain. Without moisture of this kind it appears that no 

 infection can take place, although all the other conditions may be favorable. 

 Atmospheric dryness not only limits spore germination, but retards the secidial 

 development of the fungus as well as the growth of the mycelium. If moisture con- 

 ditions subsequently occur, spores are produced, otherwise the mycelium finally dies. 

 The uredo development of the fungus is similarly checked, changing to a production 

 of teleutospores without regard to season or condition of the host. The teleuto stage 

 of the fungus is independent of food supply, moisture, temperature, or season. In 

 most sections of the country extremes of moisture conditions are insufficient to bring 

 out the points above enumerated. 



In addition to the direct relation of moisture, there are important indirect rela- 

 tions which pertain mostly to soil moisture. An abundance of soil moisture during 

 the summer has a marked effect in retarding the development-of the fungus by giv- 

 ing the host greater vitality and resistance. This is shown by the varying summer 

 rainfall in different seasons, by the differences in water-retaining capacity of different 

 soils, and the effect of irrigation on the occurrence of the disease. 



A study of Cystopus candidus, A. Eberhardt (Centbl. Bakt. u. Par., 2. Abt., 12 

 [1904), Nos. 6-8, pp. 235-245; 11-16, pp. 426-439; 19-21, pp. 614-631; 22-24, pp. 

 714-725, pi. 1). — The author presents an elaborate report of" investigations on the 

 morphological and histological changes in the host plants as well as the results of 

 investigations on the specialization of the mildew of cruciferous plants, Cystopus can- 

 did nn. The changes in the host plants caused by the fungus are described at consid- 

 erable length, comparisons being made as far as possible with those produced by the 

 downy mildew (Peronospora parasitica) . A large range of host plants was studied, 

 and among the phenomena noted as caused by the fungus are the hypertrophy of 

 all the tissues attacked, the swellings occurring on all parts of the plant except the 

 roots and rarely on the ovules, the atrophy of ovules and pollen, the formation of 



