ECOLOGICAL GKOUPS 493 



449. Practical applications of the knowledge of light require- 

 ments. A few words have already been said (Sect. 370) about 

 the importance of recognizing the difference in the light re- 

 quirement of trees. The farmer and the horticulturist often 

 have need of considering the light requirements of cultivated 

 plants. It is not infrequently desirable to grow some kind of 

 crop in partial shade, as in a young orchard. In such situa- 

 tions some of the plants which bear small fruits, as raspberries, 

 blackberries, 1 and strawberries, will succeed fairly well. So 

 also will common beans and broad or horse beans. Pumpkins 

 and squashes grow well in cornfields. A good many useful 

 grasses are tolerant of shade, and mixtures of grass seed suit- 

 able for lawns under shade trees are sold by the principal 

 seedsmen. Some of the grasses of more or less value for 

 pasture or hay, which grow in moderate shade, are Kentucky 

 blue grass, 2 Canada blue grass, 3 orchard grass, 4 rough-stalked 

 meadow grass, 5 wood meadow grass, 6 crested dog's-tail, 7 and 

 sheep's fescue. 8 



Some crops, as sugar beets, are of inferior quality when 

 grown in partial shade. In Austria-Hungary the beets grown 

 in the sun were found by one observer to average rather more 

 than three times the weight of those grown in the shade. Add 

 to this the fact that the sun-grown beets contained about 

 1J per cent more sugar than the shade-grown ones, and the 

 importance of full sunlight for the sugar-beet crop becomes 

 very apparent. Certain crops depend for complete success 

 upon a long series of days of the most brilliant sunshine. 



1 The amount of shade which can be tolerated by plants of the same 

 genus, natives of the same region, often differs widely. The black raspberry 

 (Rubus occidentalis) has been found to flower freely but to mature hardly 

 any fruit in a situation where the bushes were so shaded that during the 

 earlier half of the day they received but one twelfth to one fifteenth of the 

 total sunlight, although they had full sunlight during most of the after- 

 noon. Mixed with these bushes were blackberries (perhaps a cultivated 

 form of R. allegheniensis) which flowered and fruited abundantly. 



2 Poa pratensis. 8 Poa compressa. 4 Dactylis glomerata. * Poa 

 trivialis. 6 Poa nemoralis. 7 Cynosurus cristatus. 8 Festuca omna. 



