316 THE POPULAR SCIENCE MONTHLY 



I wish to state at the start that I have made an effort to collect 

 notes bearing against this theory as well as for it. What I have here 

 to offer is merely a report, almost statistical in its aim and methods, 

 on the general significance of the total number of researches which have 

 thus far been made touching upon modification. Original papers have 

 been occasionally consulted, but the major portion of the notes are 

 drawn from the well-known text-books dealing with these questions 

 and have been rearranged, after a new scheme, under headings ex- 

 pressing in a general way phylogenetic rank. Text-books subdivide the 

 experiments according to the external agents employed, e. g., food, light, 

 heat, gravity, etc., or discuss special types of modification in a dis- 

 jointed way. The headings that I have made use of are: Plants, Low 

 Metazoa, Mollusks, Crustaceans, Insects, etc., Fishes, Amphibians, 

 Reptiles and Birds and Mammals, and finally Mental and Moral Traits. 



It is of course impossible to say at times whether a certain species 

 is higher or lower than another species, but surely we may expect agree- 

 ment if we say that mammals are higher than birds, that the amniota 

 are higher than the anamniota, and that amphibians are higher than 

 fishes, and that all vertebrates are higher than the low invertebrates. 

 It would be difficult to agree as to the relative rank of the highest of the 

 invertebrates and the lower vertebrates, and difficult to compare the 

 higher plants with low metazoa, but enough of relative rank will be 

 admitted for the purposes of this generalization. Let us now see what 

 chief modifications have been produced (that are nevertheless com- 

 patible with life) in these various organic groups. 



Plants 



The modifications in the plant world are so numerous and so strik- 

 ing that one scarcely needs to mention more than a small portion of all 

 the experiments to show that plants are greatly influenced by their 

 surroundings. For instance, plants may be made to grow ten or even 

 twenty times as fast under optimum conditions as compared with their 

 growth under the least favorable. 3 The Japanese dwarf trees show 

 in a remarkable way the possibilities in this direction. The effect 

 is due in part to a mechanical process which prevents the spreading of 

 the branches, but the chief cause is found in poor soil and lack of 

 nourishment. 4 



The great influence of gravity on the direction of the development 

 of different parts of plants is also well known, as is their power of 

 regeneration, where a single begonia leaf may produce a new plant, 

 and even flowers if set in moist sand. 5 The great effect of differences 



3 C. B. Davenport, "Exp. Morph.," pp. 451-452. 

 *De Varigny, "Exp. Evolution," p. 71. 

 5 Morgan, " Regeneration," p. 74. 



