45 . 



A METHOD OF TEACHING THE EVOLUTION OF THE 

 LAND PLANTS 



By B. W. Wells. 



One of the betes noires of elementary botany instruction is the 

 problem of getting across the story of land plant evolution with 

 its complicatfons arising out of the alternation-of-generations 

 situation. I suppose it is safe to say that the majority of stu- 

 dents who survive freshman botany do not really grasp the facts 

 of the complete reversal in the food relations of the two genera- 

 tions, the progressive differentiation associated with sex and other 

 fundamental generalities which are familiar to the advanced 

 botanical student. 



This failure is primarily due to the fact that the types are 

 taken up one at a time with no genuine opportunity afforded to 

 bring all of the significant types together so they may be auto- 

 matically compared ; for only the comparative method constitutes 

 the vital approach to such an evolutionary problem. 



The writer a number of years ago overcame in great part. the 

 above mentioned weakness in his teaching by introducing the con- 

 centric method of handling the life cycles. 



Professor J. H. Schaffner, of Ohio State University, first used 

 the diagrammatic method of presenting the life history of plants 

 by arranging the significant stages at intervals in a circle. These 

 intervals are marked out by radii. And those used by the writer 

 are the ones suggested by him in his Laboratory Guide. 



The writer's adaptation of Schafifner's method is involved in 

 requiring the student to draw the life cycles of the type plants in 

 a concentric manner, the lowest in the scale of evolution at the 

 center, the next higher around this, and so on. For this purpose 

 they are furnished a large durable sheet of paper, such as an un- 

 folded genus cover. After the student has finished his laboratory 

 and text study of a liverwort (preferably Ricciocarpus) he is 

 introduced to the life cycle method by furnishing him the neces- 

 sary sketches or the finished cycle, which he is at liberty to copy 



