1905.] DISEL\SES OF THE POTATO IN CONNECTICUT. 1 33 



tion when the caustic action on the foliage results. The tip 

 burn trouble mentioned is purely physiological, due to the foli- 

 age at its margin being unable in times of drought to replace 

 and check the transpiration of water, consequently the tissues 

 here turn yellow, roll up, and finally die. This trouble is not 

 so common here as it is in some of the States of the middle 

 west, since moisture is more evenly distributed during our 

 growing season. 



2. The Scab fungus apparently confines its attack to the 

 tubers, where it produces a superficial, corroded, or " scabby " 

 condition of*the skin. The presence of the fungus acts as an 

 irritant, and as a result an unusual development of corky tissue 

 results. This growth of cork cells not only helps to protect 

 the tuber from the scab fungus but it is also helpful in keeping 

 out other fungi and bacteria that would cause subsequent 

 rotting. Scabby potatoes, apparently, are not much more 

 subject to rot than are those free from scab. 



Scabby potatoes occur all over the world, and many theo- 

 ries have been advanced as to their cause, but it was not until 

 Professor Thaxter, the first botanist of the New Haven station, 

 studied the trouble that the true cause was shown. The fungus 

 is sometimes seen on the scabby spots as a faint grayish mold 

 that appears most prominent when the tubers are freshly dug. 

 It is very simple in structure and easily breaks up into bacteria- 

 like rods. It can also live in the soil and its development there 

 is favored if this be slightly alkaline, instead of acid, and by the 

 presence of manure. Other root crops, such as beets and 

 turnips, are attacked, so that rotation of these with potatoes is 

 not desirable. 



The most efficient preventive measures now known are 

 selection of land as free as possible from the fungus ; proper 

 rotation of crops ; the use of clean seed ; the careful use of ani- 

 mal manure if scab has proved troublesome ; avoiding liming 

 land used for potatoes ; and seed treatment with formalin or 

 corrosive sublimate. This latter process consists in soaking the 

 tubers for about one and a half hours in corrosive sublimate 

 (one pound to 50 gallons of water), or in formalin (one pound 

 to 30 gallons of water). To get the best results treated seed 

 should be planted on land free from the fungus and but little 

 manure used. 



3. The Rosette or RJiizoctonia disease has lately come into 



