542 



SCIENCE 



[N. S. Vol. XXVI. No. 669 



An important duty in this new century 

 will be to develop a better appreciation and 

 more accurate understanding of the rela- 

 tion of these factors to health and disease. 

 The cropping system of a farm or orchard, 

 the planting of a nursery or a park to be 

 satisfactory and successful in securing 

 healthy growth must be undertaken only 

 after a careful consideration of all these 

 factors involved. Like the architect, the 

 horticulturist and the farmer must have a 

 carefully thought-out plan and as nearly as 

 possible see the end from the beginning. 



RESISTANCE AJSTD IMMUNITY 



Our ideal, of course, is to cultivate plants 

 that can in the largest measure consistent 

 with other requirements fight their own 

 battles. Observation and experience have 

 given us a large amount of information on 

 adaptability to conditions and resistance .to 

 disease, which remains to be classified and 

 digested in order to be made generally 

 available. We often neglect to reap the 

 benefits of a destructive drouth, a cold wave, 

 an epidemic of disease, or the failure of a 

 crop, by neglecting to study and save what 

 is left. The few straggling plants left do 

 not appeal to the average man. He plows 

 them up or turns in the hogs. But the 

 man familiar with nature's methods sees 

 in these survivors resistant strains and 

 saves the few straggling plants for seed, 

 with the hope that the few survivors may 

 have some peculiarity transmittable to 

 progeny, making them resistant to the 

 factor that caused the general destruction 

 of the crop. In this way originated the 

 wilt-resistant cotton, wilt-resistant cowpeas 

 and flax, and cowpeas and tobacco resistant 

 to nematode or root-knot. Strains of red- 

 clover resistant to anthracnose (a disease 

 which in many sections of the South makes 

 it impossible to grow ordinary non-resistant 

 clover) were also originated in this way. 

 Strains of corn, oats, wheat, rye, clover. 



alfalfa, sugar beets and other grains, forage 

 plants and vegetables resistant to cold, 

 alkali and drouth have been developed 

 from such selections — in some cases made 

 purposely by subjecting the crop to these 

 conditions, in others in simply taking ad- 

 vantage of what occurred naturally. In 

 some of the older and more thickly popu- 

 lated parts of the world, necessity has 

 forced the saving of the last straw. This 

 is why we find the drouth-resistant durum 

 wheats in the dry regions of Russia and 

 Asia and around the Mediterranean, the 

 alkali and drouth-resistant alfalfas and 

 other forage crops in the same regions, a 

 cold-resistant alfalfa in Siberia and North- 

 ern Manchuria, the cold-resistant winter- 

 wheats of Russia, and other crops too 

 numerous to mention. Hundreds of years 

 of culture and selection, forced by poverty 

 and necessity under forbidding conditions 

 of cold and drouth and disease, have made 

 those sections veritable storehouses of good 

 things, but what nature and necessity have 

 not produced for us we can in large meas- 

 ure do for ourselves. We can combine the 

 cold-resisting quality of the trifoliate in- 

 edible orange with the fruit qualities of the 

 tender, sweet orange; the disease-resistant 

 quality of the citron with the fruit quality 

 of the edible melons; the rust-resistant 

 quality of the durum wheat with the berry 

 of the blue stem; the cold-resistant quality 

 of the wild crab with the fruit of our finer 

 apples. The possibilities of such composite 

 breeding have scarcely been toviched or ap- 

 preciated. In such work many factors 

 must be taken into account and great care 

 and foresight exercised. 



PATHOLOGICAL INVESTIGATION 



Coming now to the scientific study of 

 plant diseases, there is almost unlimited 

 room for improvement. Compared with 

 what there is still to discover, our knowl- 

 edge of most diseases is still meager and 



