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SCIENCE 



N. S. Vol. XXVII. No. 



veloped in such cases is determined by the 

 balance of water supply, conducting 

 capacity of the shoot, and the transpira- 

 tion rate. The combined action of these 

 factors does lead to the formation of 

 organs in many instances that have the 

 aspect of being of increased fitness and 

 efficiency, but results of the opposite char- 

 acter are encountered. Thus, in my own 

 experiments with Boripa, the American 

 watercress, it was seen to bear filiform, 

 dissected leaves when submerged, linear 

 dissected leaves when emersed, but when 

 acclimatized at the Desert Laboratory, de- 

 veloped broadly ovate, almost entire, 

 laminse. 



Etiolation resulting from diminished 

 illumination or total deprivation of light 

 has been supposed to induce adaptive 

 elongation of stems and petioles by which 

 the chlorophyll-bearing tissues were car- 

 ried past obstacles which cut off the light. 

 Long-continued experimental studies have 

 demonstrated that not half of the species 

 tested exhibit such elongation, a greater 

 number showing thickened organs, and 

 other useless alterations. 



Illustrations might be multiplied, and a 

 candid estimate of the alterations under- 

 gone by the organs of a plant when it is 

 subjected to unusual conditions of tem- 

 perature, moisture, food-supply and sea- 

 sonal change usually fails to reveal any- 

 thing more than a coincidence of direct re- 

 sponse and useful purpose, and it is evi- 

 dent that such coincidences must be sub- 

 jected to the closest scrutiny before being 

 accepted as adjustments conditioned by 

 suitability. 



Turning now to structures and func- 

 tions of a specialized character, normally 

 heritable and characteristic, it is easy to 

 read into them a fitness not actually pres- 

 ent, or not possible of causal induction by 

 the factors to which they are supposed to 

 be an adaptation. Thus but recently the 



investigations of Lloyd complete the proof 

 that the movements of stomata are not 

 adaptive or regulatory with respect to 

 transpiration. Reams have been written 

 as to the automatic and finely balanced 

 valve-like action of these organs with re- 

 spect to the conservation of water in the 

 plant, yet it is now known that they open, 

 widen and close in response to other 

 stimuli rather than those arising from the 

 turgidity of leaves and the aridity or 

 humidity of the air. The presence of 

 spines and spiculse on cacti serve to check 

 the depredations of grazing animals, but it 

 would need a devious logic to conjure up a 

 causal relation between the two. These 

 structures are probably due to aridity, but 

 are not in themselves a useful structure in 

 adaptation to this condition: a dozen 

 species of cacti, devoid of spines altogether, 

 are known which live under the most 

 accentuated desert conditions. Morgan 

 also concludes that the capacity of re- 

 generation has been developed without re- 

 gard to any directly adaptive action, and 

 this exemplification might be extended in- 

 definitely if space permitted. It is not in- 

 tended to assert the non-existence of direct 

 useful alterations in the organs of plants, 

 and of the functions they serve: Instances 

 of apparent validity are numerous, par- 

 ticularly in rhythmical activities of all 

 kinds, but the entire matter of causal 

 adaptation is in need of a basal reinvesti- 

 gation from an entirely new view-point. 



This leads to a second problem most 

 readily suggested by the time-worn phrase 

 "inheritance of acquired characters," a 

 conception so vague, so widely inclusive 

 and withal so illy consonant in ordinary 

 usage with the facts, that it will soon be 

 quoted only for its historical importance. 

 If by this phrase is meant that an organism 

 makes adaptive response to its environment 

 by adjustments of functions followed by 

 alterations of structure, and that the con- 



