Iarch 25, 1921] 



SCIENCE 



273 



An obvious rejoinder is that is is the ap- 

 plied science that keeps the investigator alive. 

 So far as plant culture is concerned, it existed 

 thousands of years before there vs'ere such a 

 thing' as pure or fundamental science, unless 

 I mistake vrhat is meant by this phrase. 

 Clearly the quotation asserts too much, if 

 plant culture is part of " applied science." 



The statement that plant culture is made 

 up largely of botany is objectionable, first of 

 all because it is offensively patronizing and 

 second because it is to a great extent not true. 

 The plant culturist, be he agronomist, horti- 

 culturist, forester, or what not, is concerned 

 first of all in the methods that make for the 

 successful culture of a plant, and secondarily 

 in the factors or factor complexes that aSect 

 quantity or quality of yield. Yield, includ- 

 ing the underlying factors, is the central con- 

 sideration in plant culture, but the word yield 

 is seldom seen in a botanical text-book. In 

 the culture of crops there are four major 

 series of factors that affect yield, namely, the 

 adaptations of the plant, the quality of the 

 soil, the climatic factors, the cultural or arti- 

 ficial factors. It is a fair assumption that if 

 the best adapted variety be planted on rich 

 soil and intelligently cultivated the highest 

 yields are to be expected if the weather condi- 

 tion are favorable and pest injury reduced to 

 a minimum. It is worth while considering 

 briefly just how much we know concerning 

 the relation of yield to a few of the factor 

 complexes mentioned. 



Consider first the plant and its habits, or if 

 you prefer its ecological adaptations. Un- 

 doubtedly primitive man, like the modern 

 grower of orchids, attempted when he first 

 cultivated a plant to imitate its natural 

 habitat. He certainly did not plant rice on 

 the dry hilltops nor wheat in the marshes. 

 But what after all do we know about these 

 habital adaptations save by observation. No 

 sensible man would expect to succeed with 

 bananas outdoors in ~New England. But just 

 why is it, if you please, that bananas can not 

 stand as much cold as apple trees? Or con- 

 sider a simpler case, namely winter wheat 

 and spring wheat, perhaps representing the 



broadest extremes in a single species of phys- 

 iological adaptation in relation to temperature 

 that has been developed in plant culture. 

 Just why does the one endure much lower 

 temperatures than the other? It would seem 

 practically certain that the difierences are not 

 due to any morphological character, since 

 similar phenomena occur in naked organisms; 

 therefore, it is nearly certain the differences in 

 adaptation lie in the protoplasm. But it must 

 be admitted we have not even a working 

 hypothesis as to the nature of the machinery. 

 Again consider the behavior of some intro- 

 duced plants with that of others brought from 

 the same region. Bluegrass, redtop and white 

 clover have spread over all of the northeastern 

 fourth of the United States and tend quickly 

 to occupy all cleared and untilled land; in 

 other words, they spread aggressively. In 

 contrast, certain other common European 

 grasses can barely exist or do not thrive at 

 all. Crested dog's-tail is rather a botanical 

 rarity in the United States notwithstanding 

 that thousands of pounds of seed are sovsm 

 annually, just because the English consider 

 it a good grass. StiU more remarkable is 

 Weingartneria canescens, a grass the viable 

 seed of which is an abundant impurity in 

 certain European seeds, but no one has ever 

 found a specimen of the plant in the United 

 States. Japan clover, introduced accidentally 

 about 1853, has spread over all the south. 

 The lowland ranges of California are covered 

 with grasses and other herbs, 80 per cent, of 

 the bulk of which is made up of Mediter- 

 ranean plants. On the foothills of the Hima- 

 layas the Mexican dahlia escaped cultivation 

 and now covers miles of the mountain sides. 

 In Ceylon and Java an extremely aggressive 

 and abundant sunflower-like plant is Tithonia 

 diversifolia, which in its native home near 

 Acapulco, Mexico, is a very restricted rather 

 rare plant. Many other cases might be cited. 

 Why are some of these introduced plants so 

 aggressive and others so impotent? It is an 

 evident fact and a clear problem of much 

 importance agriculturally. All that we can 

 postulate is that as a rule an introduced 

 plant that is aggressive comes from a region 



