476 SPECIAL PLANT PATHOLOGY 



access to the most important work which has been done. In this inves- 

 tigation, the student should write descriptions of the diseased host 

 plants and parasitic organisms concerned, according to the method out- 

 lined in part IV, pages 639 to 642, and together with this detailed de- 

 scription he should compile a bibliography. 



Pedagogically it is a mistake to give too full details in a text-book, 

 because the student learns to depend on the statements in the book 

 rather than on original observations of his own. The compilation of a 

 bibliography becomes an important adjunct to all successful phyto- 

 pathologic work. "Study things, not books" is a truism in this depart- 

 ment of scientific knowledge, as in other departments of natural science. 

 The teacher should so guide and stimulate the class of students that each 

 member of the class will be led to independent study and investigation, 

 so that they may be able to apply individually the modicum of knowledge 

 which the strictures of the time allotted to the subject in the college has 

 permitted them to obtain. Unless this independence of thought and 

 action is secured, the results of the teaching have not been satisfactory. 

 It is, therefore, hoped by the writer of this text-book that what has been 

 included in its pages will be directive and helpful to teacher and student 

 rather than a work of encyclopedic value. The subject of phytopa- 

 thology is such a vast one, that it would be impossible without the coop- 

 eration of a large number of specialists to make a work which would be 

 of encyclopedic value. The design of this text-book has been to give an 

 outline of the subject, so that the attention of the student may be direc- 

 ted to the important phases of the subject of phytopathology. 



Alfalfa {Mcdicago sativa L.) 



Leaf-spot {Pseudopeziza medicaginis (Lib.), Sacc). — The fungus 

 which causes this widely prevalent disease, where alfalfa is grown, 

 belongs to a genus in which the apothecium is formed beneath the epi- 

 dermis and as it grows it breaks through the epidermal covering and 

 emerges as a shallow, relatively simple structure with asci that contain 

 eight one-celled spores. It is related to a similar fungus Ps. trifolii, 

 which attacks the leaves of clovers. It forms small brown, or black, 

 spots on the upper leaf surface usually. These spots, which are about 

 2 mm. in diameter, represent the sessile apothecia, which are sprinkled 

 pretty copiously over the leaf surface in the latter part of summer. 



