DrSKASES OF PLANTS. 553 



Cotton ^TowtTs arc uri^cd to loUow <nit this selection, as it sinnns to be om; of 

 the most proiuisiii.t; inctliods of coiiibatiui; the diseasi^-. The rotation of crops is 

 also reconiiucnded. 



The relation of nematodes to the disease is pointed out, th(! authors ehiimin;,' 

 that the presence of nematodes aids in its develoiunent. 



A new alfalfa disease, W. Paddock (Colorado Sta. Press Bui. 2S, pp. 2). — A 

 brief account is u'iven of a disease of alfalfa that has caused cousideral)le 

 damaj,'e in a iiunil.cr nf lo.alities in Colorado. In June, 1900, the author had 

 the opportunity of inspecting infected fields during the growing season. The 

 cause of the injury was aitpai'ent, as shown by the occurrence of numerous 

 blackened stems from which a thick juice was oozing, plainly indicating that 

 the plants were suffering from a bacterial blight. Sul)se(iueut examination 

 showed that this was the probable cause of the disease. 



The first evidence of disease to be noticed is a short, weak, light-colored 

 growth of the lirst croii. the stems seldom averaging more than a foot in height 

 at the time the first cutting is made. A close examinatitm shows that the 

 majority of these stems are discolored and are very brittle. The disease appar- 

 ently does not kill many plants the first year, but in course of time so many 

 plants die that the fields become useless. 



Almost nothing is known of the blight as yet, and the horticultural section of 

 the station solicits <'orrespondence regarding its occurrence. 



Potato leaf curl (Roi/. Hot. Gard. Ken,' Bill. Misc. Inform., 1906, No. 7. pp. 

 2.'/2-2//.7).— After describing the leaf curl of potatoes, due to Macmsporimn 

 solan i. attention is called to the fact that the fungus is perpetuated from year 

 to year by mycelium' in the tubers. When infested tubers are planted the 

 mycelium grows along with the stem and enters the leaves, and also passes 

 down into the young tubers. When only slightly infested with mycelium the 

 further development in the tissues of the potato plant will depend on the 

 weather conditions. It may do little harm beyond infecting the new tubers. 

 or, if conditions are favorable, develop into an epidemic form and destroy the 

 infested portions of the potato plant. 



The fungus mycelium does not destroy the starch of the tul)er, but lives 

 only on the proteid substances, and it is practically imp(>ssil)le to tell l)y 

 superficial methods whether a tuber is killed or not. 



Owing to the fact that the conidia of the fungus are only produced on dead 

 or dying plants, the epidemic is not increased by healthy plants having their 

 foliage infested Iiy the conidia, as in the potato blight. Young shoots may be 

 infected late in the season, but the infection remains local and does not 

 extend to the tuV)ers. According to the author, the infection can only tal;e 

 place through the tuber, and this can be brought about either by planting 

 diseased tubers or from conidia present in the soil. 



A series of experiments has shown that the mininumi temperature for germi- 

 nation of conidia is 47° F.. with a maximum of 78° and an oi)timum of 64°. 

 It is claimed that the resting spores of the fungus have germinated after 

 having been kept in the laboratory for (5 months in a perfectly dry condition, 

 and it is quite j)robable that they remain in the soil fi'om one season to another 

 without losing their power of germination. 



Comparative studies have been made with the leaf curl of tomato (J/ac;o- 

 sporiuw tomato), and inoculation experiments have proved that the two fungi 

 are identical, the conidia from the tomato infecting potato plants and vice 

 versa. 



.\s pracliiai means for couibatiiig these diseases, the author recommends 

 planting potatoes from districts free from disease. The potatoes should not 



