TEACHING AND LEARNING 17 



of correctness. This spirit is in direct contradiction to that 

 of reliance upon the conservation of energy and of matter, though 

 the latter is a chief mark of the scientific mind. Again, we have 

 the primitive tendency to link together by some mysterious 

 bond of cause and effect any two striking things which come 

 to occupy our attention simultaneously, though in fact they 

 may be only accidentally or coincidentally connected. Again, 

 the defensive instinct leads us to interpret everything in the direc- 

 tion of self-justification or self-magnification, to warp obser- 

 vation into support of preconceived ideas, and to magnify the 

 importance of any new thing discovered by ourselves to the dis- 

 paragement of the old as expounded by others. Again, we have 

 the old habit of following blindly our constituted leaders, whence 

 arises altogether too great reliance upon authority, especially 

 of the eminent. And we have always a primitive delight in 

 wonders, and corresponding willingness to believe in them, 

 and an ever-present predilection for pleasing fiction over com- 

 monplace fact. All these peculiarities of the mind are quite 

 in harmony with its use in the struggle for material existence, 

 but they are frailties when it is applied to scientific investigation. 

 They tend ever to warp the judgment from the objective towards 

 the subjective, and against them the student must learn to be 

 ever upon guard. This applies to the use of mind as it is, and 

 is wholly apart from the possibility that some of the phenomena 

 of Nature may be of a kind which we have neither the senses 

 to perceive nor the mental equipment to apprehend. 



Such are the more important working principles and pre- 

 cautions needed in Plant Physiology. If the student cares to 

 learn more of scientific logic and method, he will find the fullest 

 satisfaction in an admirable work, " The Grammar of Science," 

 by Karl Pearson (London, Second Edition, 1900). And 

 the errors of the mind of man were long ago set forth with great 

 power by Bacon as The Idols in his " Novum Organum." 



To discover new facts is not the whole duty of the scientific 

 man. It is also a part of his task to communicate them to 

 his fellows. And so the student, aside altogether from the 



