176 



SCIENCE 



[N. S. Vol. XXXIII. No. 840 



tinetion. A species might have enormqus 

 potential adaptability; but it would be- 

 come extinct if the death-rate were too 

 high in comparison with the rate of adap- 

 tion. This principle is made use of in the 

 fight against weeds. "- 



Weeds, like other plants, grow where they can 

 find room; and the more room any plant can find, 

 other things being the same, the farther and more 

 rapidly it will spread over the earth. But room, 

 used in this connection, does not mean, entirely, 

 space vacant of other plants, but rather conditions 

 of competition into which the given plant can fit 

 itself with prosperity. Ground may be covered 

 with a given plant, and yet a species of wholly 

 different character and habits may thrive along 

 with it. This is well illustrated in the growth of 

 twining or climbing vines in dense thickets of 

 shrubbery, or the practise, common even with the 

 Indians, of growing pumpkins in corn fields. If 

 weeds, then, are to be kept out of grounds, the 

 land must not only be occupied with some other 

 crops, but with a crop which will not allow the 

 weed to grow along with it. In practise, it is 

 impossible to select all crops from plants which 

 so completely encumber the ground that no in- 

 truder can find a foothold; but this disadvantage 

 is readily and almost wholly overcome by means 

 of the rotation of crops — one crop in the rotation 

 destroying what weeds may have crept in with 

 the preceding ones. Thorough cropping of the 

 land and judicious rotation of crops, therefore, 

 are conditions against which no weeds can stand; 

 and as these are the vital conditions, also, of 

 successful agriculture, it may be said that then 

 lands are well farmed. 



The daisy-cursed meadows of the east are those 

 which have been long mown and are badly " run," 

 or else those which were not properly made, and 

 the grass obtained but a poor start. The farmer 

 may say that the daisies have " run out " the 

 grass, but the fact is that the meadow began to 

 fail, and the daisies quickly seized upon the op- 

 portunity to gain a foothold; and just so long as 

 the farmer persists in his accustomed methods will 

 the daisies usurp the land. The weedy lawns are 

 those which have a thin turf, and the best treat- 

 ment is to scratch the ground lightly with an 

 iron-toothed rake, apply fertilizer and sow more 

 seed; in other words, augment the struggle for 

 existence, and the weeds will go down before the 



== Cf. Bailey, " The Survival of the Unlike," 194, 

 196, 1896. 



June grass, and the grass plants themselves, be- 

 cause of the greater numbers, will be more slen- 

 der and will make a softer turf. 



ATTITUDE OP BIOLOGISTS 



It may be asked to what extent biologists 

 make use of the theorem of Le Chatelier as 

 a working hypothesis in studying the effect 

 of external conditions. So far as I can 

 learn, nobody makes any active use of it, 

 and many biologists would deny the appli- 

 cability of the theorem. 



Darwin"'' began by attributing very little 

 to the direct action of the climate, etc. : but 

 later he stated that more weight should 

 have been allowed to the direct action of 

 the environment, i. e., food, climate, etc., 

 independently of natural selection. He 

 says"* that it is "probable that variability 

 is directly or indirectly caused by changed 

 conditions of life. Or, to put the case 

 under another point of view, if it were 

 possible to expose all the individuals of a 

 species during many generations to abso- 

 lutely uniform conditions of life, there 

 would be no variability. ' ' In spite of this 

 he states'" explicitly that long-continued 

 action of a different climate has produced 

 differences in American trees which are of 

 no especial service to them. 



Nageli's"^ "extensive cultural experi- 

 ments with alpine Hieracia led him to form 

 the opinion that the changes which are in- 

 duced by an alteration in the food-supply, 

 in climate or in habitat, are not inherited 

 and are therefore of no importance from 

 the point of view of the production of 

 species. ' ' 



°^ Cf. Schwalbe, " Darwin and Modem Science," 

 125, 1909. 



" Darwin, " Animals and Plants under Domes- 

 tication," 2d ed., 2, 242, 1890. 



" Darwin, " Animals and Plants under Domes- 

 tication," 2d ed., 2, 271, 1890. 



°* (j'f. Klebs, " Darwin and Modern Science," 

 225, 1909. 



