THE IMPORTANCE OF THE ROOT-SYSTEM 



'57 



is attained, when further growth is horizontal. Nevertheless, a grain 

 of wheat which is sown at too great a depth, even if it germinates, may not 

 be able to reach the surface, or if it does, it will suffer from a certain 

 disadvantage as compared with seedlings which germinated at a more 

 favourable depth. It is moreover easy to see why the roots may develop 

 badly or die when they are buried too deep in transplanting, or when 

 soil is heaped around the base of the stem. Practical experience tells us 

 that deeply rooting plants can more readily accommodate themselves to 

 a superficial development of the root-system, than the reverse. 



The power of adaptation is of the highest biological importance, 

 and may be so marked 

 that typical land-plants 

 can be cultivated in 

 water (Sect. 73), and 

 may even accom- 

 modate themselves to 

 the changed conditions, 

 when the roots grown 

 in soil are suddenly 

 brought into water or 

 vice versa. It is easy 

 to understand that such 

 a sudden change may 

 often produce transi- 

 tory ill effects, and that 

 when transferred from 

 water to soil, the plants 

 may wither because the 

 roots and root-hairs 

 are not in proper con- 

 tact with the particles 

 of soil. On the other 

 hand, when placed in 

 a nutrient solution, the root-hairs and root may have been injured by 

 the removal from the soil. For these and similar reasons, a number of the 

 roots die off after the transference has been made, and are gradually 

 replaced by new growths. The roots of seedlings grown in earth or 

 sawdust are not perceptibly injured when placed in water, and even 

 older roots may without doubt accommodate themselves to an aquatic 

 life 1 . Indeed, if the transference were sufficiently gradual, this would 



FlG. 14. Hordeum vulgare. a sown on the surface; b deeply buried ; 

 j = the fruit grain. About one-third natural size. 



1 Literature: Sachs, Versuchsst., 1860, Bd. n, p. 13 ; Knop, Versuchsst., 1863, Bd. v, p. 96; 

 Knop und W. Wolff, 1. c., 1865, Bd. vu, p. 345. On the anatomical differences between writer- and 



