384 The Study of Environment [Mar. 



tion which also will not stand investigation. When dandelions first 

 bloom in the spring on a golf course, they come up eight to ten 

 inches high and are promptly cut down by the lawn-mower. The 

 succeeding crops have very short stems and are unfortunately not 

 damaged by the mower. On examination, the length of the stems 

 proves to be determined much more by the intensity of the light 

 than by the danger from the lawn-mower. The real way in which 

 a tree adapts itself to onslaughts with an axe, is by developing 

 buds back of the point of attack. 



If we subject a plant to starvation and thirst by planting it in 

 a poor soil in a dry country, the adaptation consists in a larger root 

 development and in modifications which cut down the evaporation. 

 If we continue to give our hypothetical man alcoholic drinks, he will 

 probably adapt himself to the new environment to the extent that 

 it will take more liquor to make him drunk. The response to the 

 bleaching action of the light is the increased production of Chloro- 

 phyll. In all cases, it is important to make certain what is cause 

 and what is effect. An interesting instance occurs with Proser- 

 pinaca palustris as studied by Burns.^ This plant is easy of culture 

 both on land and in water. The " land type " of leaf is lanceolate 

 with serrated margins while the " water type " is finely divided, with 

 a central rib and from three to five filamentous divisions on each 

 side. A careful study brought out the fact that "the water envi- 

 ronment is not the cause of the division of the leaf. Nor does it 

 depend upon light, temperature, gaseous content of the water, or 

 the contact-stimulus as such, The only conclusion that seems justi- 

 fied by my experiments seems to be that Proserpinaca palustris has 

 two forms — an adult form and a juvenile form. Under good vege- 

 tative conditions it has a tendency to produce the adult form with 

 the entire leaf, blossom and fruit ; under poor vegetative conditions 

 it has a tendency to produce the juvenile form with the divided leaf. 

 And furthermore, a reversion to the primitive form may be caused 

 by unfavorably influencing the vegetative conditions." 



It must also be remembered that any direct development of any 

 Organ in response to external Stimulus is going to be accompanied 

 by a more or less general rearrangement throughout the System. 

 These other changes are secondary ones and may or may not be 



"Burns: Annais of Botany, 18, 579 (1904). 



