184 Causes and Course of Organic Evolution 



to grow became more dense and reduced in internodes, leaf 

 stalk, and leaf-size. Since then the experiment has been fre- 

 quently repeated, and with uniform results. 



We again conclude that the capacity for color production 

 existed in the plant, but only manifested itself when definite 

 environal stimuli started definite chemical changes that pro- 

 duced the red color. Many similar illustrations that the writer 

 has observed for color effect alone have been noted by him 

 or recorded by others. 



Similarly, were we to deal TNdth cuticular thickness, with 

 cell-size, with relative development of indurated tissue, with 

 plant habit in relation to growth, abundant and exact evidence 

 could be adduced to show that heredity includes not merely 

 characters and potentialities that may alone be evident under 

 certain environal conditions, it includes many others, for which 

 the protoplasmic machinery, or some substance under its 

 control, is perfectly adapted for its production, but which 

 appear only as material evidences, when the appropriate stimuli 

 or energy expenditures act on the tissues. 



The experimental studies of Lothelier (7^; 480), of Bonnier 

 (75; 217), of Schively (65: 220), and of many others since on 

 plant species, and the corresponding studies of zoologists — 

 not least those recent ones of Beebe (76) and of Tomier on 

 animal species — point the way to a future accurate estimation 

 of en^^ronment as a factor. 



The degree of variability of such animals as the Brine Shrimp 

 (Artemia salina) or the Axolotl (Ambly stoma tigrinum) — to use 

 rather extreme cases — so as at different periods of their lives 

 to simulate distinct genera is similarly explicable we believe. 

 Therefore it is that in any attempted definition of heredity 

 we believe it to be absolutely necessary that it should include 

 the expansive clause '*or to an environment that, within def- 

 inite limits, fails to alter its average constitution." On this 

 ]>rinciple, therefore, every species of plant or animal shows 

 a mobile or elastic adaptibility, that is at times as striking 

 as it is unexpected. It is this adaptibility, also, wliich enables 

 it, when in the egg state, to fuse with a complemental sperm 



