January, 1922. 



SCIENTIFIC AGRICULTURE. 



163 



volume as a "composite textbook,'' liis 

 reason beiiig- that "in this form it has the 

 greatest teaching value." Primarily and 

 obviously the book is for tfie student of 

 rural economics and whether used for 

 private study or for class-room purposes, 

 it gives a complete and very thorough 

 course in the subject. As a basis upon 

 which to build up a solid structure, the 

 author jhas taken the foundation prin- 

 ciples laid down in the past, and has used 

 the "discussion method" for presenting 

 the arguments for and against those prin- 

 ciples when applied to modern agricul- 

 ture. The theory involved is first clearly 

 stated and then followed up, for every 

 problem of the subject, by clear and con- 

 cise expressions of opinion upon economic 

 facts. 



For the use of higli schools which are 

 (Micouraging tlie study of agriculture, for 

 agricultural colleges giving courses in this 

 subject, for supplementing courses in 

 farm management, marketing, etc., and 

 for t^ie student of rural conditions, rural 

 business and rural advaueenient, this book 

 is invaluable. Many autliorities have con- 

 tributed to the text and these contribu- 

 tions represent "a selection of materials 

 in which economic principles are applied 

 to the practice of agriculture." The sub- 

 ject of agricultural economics is studied 

 from many angles and after beii'g care- 

 fully read one lays the volume aside feel- 

 ing that it will be often picked up a^^'ain 

 for further and more detailed study. 



The author is Professor of Agricultural 

 Economies at the Iowa State College. 



Deseases of the Potato 



By B. T. DICKSON, 

 Professor of Botany, Macdonald College. 



( Continued. ) 



GROUP 2. 



Diseases caused by Myxomycetes or 



Slime Moulds. 



There are certain organisms which have 

 not yet been definitely assigned to the an- 

 imal kingdom nor to the plant kingdom 

 because during part of the life history they 

 move, feed and grow in such a manner 

 that they are more animal-like than plant- 

 like, while the reverse is the case at re- 

 production time. Such organisms are 

 known as "Myxomycetes" and usually 

 thej' are saprophjiiic. Two, however, are 

 parasites causing diseases of considerable 

 economic importance, viz., " Club-root " of 

 cabbage, cauliflower, brocoli, etc., and 

 "Powdery scab" or "Corky scab" of po- 

 tato. This latter disease is caused by a 

 slime mould known as Spongospora suh- 

 terranea (Wallr.) Johnson. 



Powdery Scab or Corky Scab {Spongospora 



siihterranea). 

 Occurrence. 



The disease has been kno\\Ti in Europe 

 for nearly eighty years being described 

 first bv Wallroth in 1842 and it was noted 

 by Barkeley in 1846 in England. The 

 former investigator, however, considered 



that the disease was a smut. Brunchorst, 

 in Norway, in 1886 studied the disease and 

 named the causal organism Spongospora, 

 placing it among the ]\Iyxomycetes. Giis- 

 sow was the first to find the disease on this 

 continent, some potatoes with typical scab 

 spots being sent to him from several lo- 

 calities in Canada in 1912. Morse and 

 Melhus then found evidence of the exist- 

 ance of the disease in Maine in the sum- 

 mer of 1913. It is now known to be present 

 in Great Britain, Ireland, Northern and 

 Central Europe, South America, Eastern 

 Canada and in several northern localities 

 of the United States of which the most 

 important is Maine. 

 Symptoms. 



Tlie name of the causal organism indi- 

 cates that only underground parts are at- 

 tacked, namely roots, stolons and tubers. 

 Roots are affected earlier in the season 

 and on them white galls develop looking 

 remarkably like the nodules on the roots 

 of leguminous plants. Similar galls are 

 produced on the stolons and less commonly 

 on the part of the stem underground. 

 Roots of all ages may be affected. 



On the tuber the pustules begin to ap- 

 pear a little later in the season, usually 

 when the potatoes are already of a fair 



