1919] DISEASES OF PLANTS. 841 



the trouljle, and in some cases are no more than post mortem phenomena, in 

 the production of wluch such agencies as light may have been the main factors. 



Michigan plant disease survey for 1917, G. H. Coons {Ann. Rpt. Mich. 

 Acad. Sci., 20 {1918), pp. Jf25-450, pis. 10).— An account of Michigan plant 

 diseases in their relations during 1917 is prefaced by the statement that the 

 data are not yet at hand for the consideration of the fungi in the State in any 

 manner comparable to what can be done in regard to the distribution of 

 the higlier forms. Only gross similarities can be pointed out. 



It would seem that in large part the climate determines the fungus flora. 

 Of the two factors, temperature and rainfall, the former seems to be operative 

 in a broad way and the latter in a local way, influencing the annual prevalence. 

 The plant disea'sos of Michigan are practically those of the other States of the 

 same latitude. 



Plant diseases [British Guiana], C. K. Bancroft {Rpt. Dept. Sci. and Agr. 

 Brit. Guiana, 1917, pp. 50, 51). — ^Leaf disease of Para rubber {Melanopsam- 

 viopsis idci) was not so prevalent as during the previous year. Where the 

 winter condition of the trees occurs generally over the whole of the plantation 

 at the same time, few of the trees showed the disease, which thus appears un- 

 able to endure the period of rest, requiring for survival a continuous supply of 

 green trees. Indigenous rubber trees {Hcvea confusa) in some parts furnish 

 a basis for continual infection. 



Bud I'ot of coconut still prevails in certain districts. Both mango and bread- 

 fruit are subject to ripe rot, which may be avoided by spraying with Bor- 

 deaux mixture just after the fruit sets and then again three or four weeks 

 later. Witches' broom of cacao has declined during the past two years, yield- 

 ing readily to Bordeaux mixture if the brooms are also removed. The rice 

 plant so far appears resistant to disease. With the exception of smut ( TilleUa 

 horrida), the other known diseases of rice in the colony are blast {Piricularia 

 oryzw) and stem rot {Sclerotvaiii orjjzw), which are present in negligible 

 quantity. The most prevalent and only important disease of sugar cane is that 

 due to Marasmins sacchari, which affects the roots. The only two citrus dis- 

 eases of consequence are collar rot and citrus knot. 



Investigations on diseases of plants and their treatment, O. Grove {Jour. 

 Bath and Vi'cst and Soxitli. Counties Soc, 5. ser., 12 {1917-18), pp. 12Jf-lI,2, fig. 

 1).—A fruit blossom bacillus, affecting particularly blossoms and fruit spurs 

 of pear trees, has been shown to be carried by insects. The organism has also 

 been shov.'n to be fairly common in the soil not earlier than April. It was found 

 and studied in connection with roots of cabbage and other plants. 



Damping-off and collar rot of tomatoes differ only in the stage at which the 

 attack occurs. The fungus appears to be Phytophthora. The original source 

 of infection is not known, though sterilization of infected soil prevents the 

 disease. 



Good results were obtained from the 1917 experiments on control of Rhizoc- 

 tonia disease of asparagus. In studies of reversion of black currants the 

 primary cause was found to be the interference of mites with normal terminal 

 growth. 



The work with Burgundy mixture so treated as to develop copper stearate 

 appears to be the same as that described elsewhere by A. H. Lees {E. S. R., 

 40, p. 746). 



Philippine economic-plant diseases, O. A. Reinking {Philippine Jour. Sci., 

 Sect. A, 13 {1918), Nos. 4, pp. 165-216, figs. 20; 5, pp. 217-274, pis. 22, figs. 23).— 

 This compact account of Philippine plant diseases of economic importance 

 takes up the hosts alphabetically, discussing the diseases and naming causal 

 organisms where known. 



