November 18, 1904.] 



SCIENCE. 



669 



upon as a result of cultivation in temperate 

 climates is a further instance of protective 

 adaptation long ago secured in the tropics 

 by the unconscious selection of the Indians. 

 It was from the Central American region, 

 evidently, that the other upland types 

 came, but they represent an earlier stage 

 of development, or have deteriorated be- 

 cause selection for resistant qualities has 

 been relaxed in regions where the weevil 

 was absent, as in our southern states. 

 Other things being equal, the Indians 

 would undoubtedly prefer the perennial 

 'tree' cottons, which continue to be culti- 

 vated in Mexico arid Peru in localities so 

 arid as to exclude the weevils, though it 

 is not certain that they exist in Peru. 

 Possibly there has never been a connected 

 series of agricultural communities along 

 which the weevil could follow into South 

 America; the pest might never have 

 reached the United States if cotton culture 

 had not been extended into southern Texas. 

 But even if the varieties already known 

 in Texas were to be utilized as the basis of 

 selection, it is by no means beyond the 

 limits of probability that a resistant, regu- 

 larly proliferating variety could be secured 

 within a decade, or even within five years, 

 since cotton has been found to respond 

 rather promptly to selective influence. The 

 urgency of the matter would certainly 

 justify an extensive campaign of selection, 

 the problem being to find among the mil- 

 lions of plants which will be grown next 

 season, some which possess in the highest 

 degree the tendency to proliferation, and 

 to secure seeds from them. The task, how- 

 ever, is peculiar, and more difficult than 

 such experiments usually are, because 

 there is little or nothing in the way of an 

 external clue to the desired character. It 

 may be necessary to cut open each infested 

 square in succession to make sure that the 

 plant is allowing no weevil larvae to de- 

 velop. And after the most promising 



plants have been located it may be possible 

 to obtain seed from them only by artifi- 

 cially protecting them from the weevils. 

 Otherwise the best stock might be lost if 

 the weevils were very abundant. Indeed, 

 this suggests a reason why 'gelatinization' 

 has not become a fixed character already. 

 Selection thus far has only been in the 

 direction of proliferation in the bolls, since 

 the proliferation of tissue in the buds 

 would give a particular plant no advantage 

 over its neighbors in the matter of seed 

 production. It would enjoy no immunity 

 from subsequent attack because it had not 

 allowed any weevils to reach maturity. 

 "Weevils from other plants would continue 

 to come to it, and the chances of ripening 

 seeds would not be increased. There has 

 been, in other words, no selective induce- 

 ment for 'gelatinized' buds to become a 

 uniform character except as they might be 

 correlated with 'gelatinized' bolls, in spite 

 of the fact that for killing the weevil pro- 

 liferation in the buds is more important 

 than that in the bolls. 



These considerations reveal still another 

 episode of evolutionary history, and may 

 explain why it is that the variety protected 

 by the ants, and the other 'upland' types 

 which have originated in the same region, 

 have the additional protective adaptations. 

 It was only where the ants protected the 

 cotton and thus perpetuated it as a field 

 crop that these other considerations could 

 have a cumulative effect. The other ad- 

 aptations by which the tree cottons have 

 maintained a desultory existence are of 

 suggestive interest, but of apparently little 

 practical importance, since no field culture 

 of a perennial cotton seems to be main- 

 tained in any weevil-infested district. 



In eastern Guatemala the cultivation of 

 cotton as a field crop is strictly limited to 

 localities suited to the ants, where they 

 exist in such numbers as to give practical 



