TBE AMERICAN NATURALIST [Vol. XL V 



found. If they fail to survive or do not nourish in the 

 second location, they are said to have failed to adapt 

 themselves to the new conditions. Into this statement 

 may be read one more in accordance with a physiological 

 consideration of the matter to the effect that the inten- 

 sities of some of the factors present exceeded the maxima 

 of the plants in question and thus acted as limiting fac- 

 tors to their proper or full development or survival. 



The second assumption is to the effect that the altera- 

 tions displayed by a plant in newly encountered habitats 

 are adaptive and that these changes render the organism 

 displaying them better fitted to meet the conditions. 

 Some reactions are of such a nature as to be of benefit 

 to the plant displaying them, I nit the worker who assumes 

 that this is true of all changes even in species which 

 thrive and luxuriate in the new habitats will soon find 

 himself widely afield from facts capable of being substan- 

 tiated by experiments. Thus in the case of the Scrophur 

 laria noted above, the new maritime habitat includes a 

 congerie of agencies which incite it to form enormous 

 clusters of thickened roots and to exhibit the habit of 

 branching densely. So many branches are formed in fact 

 that the conducting channels at the base of the shoot 

 are incapable of carrying a supply of water adequate to 

 the transpiratory needs of the foliar organs, although the 

 vastly increased balance in the root-system would be suf- 

 ficient to meet the needs of the plant for days, and con- 

 sequently the widely spreading shoots of these plants 

 show a large proportion of branches which have about 

 reached maturity and are dying. The behavior of the 

 semi-spineless opuntia (0. santa rita) offers illustration 

 of the same sort. Bearing only a few or no spines in 

 its native mountains, the new segments in the cool 

 foggy climate of Carmel are spinose at almost every 

 areole. Here the result is very plainly one of the awak- 

 ening of a latency, since it seems fairly clear that this 

 plant and all of its relatives show spines as a final stage 

 in the reduction of the shoot system, and that the spine- 

 less form is the culmination of a line of progress. The 



