Page:Popular Science Monthly Volume 76.djvu/320

316 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 expressing 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 disjointed 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 agreement 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 compatible with life) in these various organic groups.

The modifications in the plant world are so numerous and so striking 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. 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.

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. The great effect of differences