DISEASES OF PLANTS. 847 



cens at 35° C.) ; (c) saprophytes, which can flourish and infect only through 

 dead material (as Bacillus amylobacter) ; and (d) faculative parasites, that is, 

 the adapted plant-infecting races of generally harmless saprophytes (as Bac- 

 terium xantlwcMorum n. sp.). These soft rots show various forms, attacking 

 either tubers or stems. 



B. xnnthochlorum n. sp. is a plant-pathogenic parallel of the harmless sapro- 

 phyte B. fluoresccns from which it appears to have developed phylogenetically 

 through the altered conditions due to culture. It is able through wounds to 

 infect potatoes, vetch, and lupines. It secretes a series of enzyms and toxins 

 which kill the protoplasm of the plants attacked. Rot of the tubers follows 

 wound infection only. The bacteria do not enter the plant by way of the lenti- 

 cels but may invade the leaves through the stomata when the loaves are wet. 



B. phytophthorum causes blackleg through infected tubers, as well as the 

 wound infection of the stem, with or without aid from insects. 



B. atrosepticum produces a dry rot of tubers, but at ordinary temperatures 

 does not attack the stems. The most resistant tubers are those which form a 

 wound-cork layer within about 24 hours after being injured. 



A bibliography is appended. 



A bacterial disease of the potato plant in Ireland, G. H. Pethybridge (Gard. 

 Chron., 3. so:, 50 {1911), No. 1290, pp. 199, 200).— A description is given of a 

 disease of the potato plant, including the tubers, in Ireland, due to Bacillus 

 melanogenes, a preliminary account of which has already been given (E. S. R., 

 25, p. 454). 



On the cause of blindness in potato tubers, Elizabeth Dale {Ann. Bot. 

 [Londoni, 26 {1912), No. 101, pp. 129-131). — This disease is so called on account 

 of its completely destroying the eyes of tubers so that they are worthless for 

 seed. The mycelium of the fungus Verticilliumi albo-atrum was found present 

 in the blind potato tubers. It grows up into the new shoots when they are 

 formed, and in some cases may pass into the subaerial shoots. In other cases 

 it never goes beyond the subterranean stems and it creeps along them into the 

 newly formed tubers. If a blind tuber is cut across, the disease may be seen to 

 be confined exclusively to the eyes and to a narrow zone immediately below the 

 cortex. The tubers may be infected by means of vegetative mycelium only, 

 without the formation of any kind of spore. Tubers have been grown for 3 

 successive years from the original diseased crop, and in each year some have 

 been blind and have had a warty, corky outer surface. 



A bacterial disease of potato leaves, Elizabeth Dale (Ann. Bot. [London'\, 

 26 {1912), No. 101, pp. 133-15 Jf, pis. 2).— In the course of investigating the 

 cause of blindness in potatoes (see above) the author found a second disease 

 which proved to be due to bacteria and quite independent of the fungus. In 

 this disease the plants almost invariably show marked symptoms of leaf curl. 



In 1910 and 1911 the disease appeared spontaneously in plants grown in pots 

 in a cool greenhouse. A study was made of them showing that the trouble was 

 due to bacteria which, are apparently different from those previously described 

 as pathogenic to the potato. The name Bacillus tuhifex n. sp. is given this 

 organism, which is technically described. The disease seems to be of little 

 practical importance, as a dry, hot summer would render the cuticle of the 

 potato leaves too thick to allow penetration by the organism. The disease so 

 far has been most marked in plants grown in a cool greenhouse. 



Experiments with potatoes resistant to wart disease {Jour. Bd. Agr. [Lon- 

 don], 18 {1912), No. 11, pp. 9-?5-9i9).— Experiments begun in 1910 to test the 

 power of resisting the wart disease by various varieties of potatoes were re- 

 ported in 1911, and in 18 centers where wart disease is known to have been 

 recently present, and in most cases the soil badly infected, potatoes were planted 



