THE STEMS 



79 



dry warm seasons, they readily become laid after a heavy shower when 

 grown at Reading. 



Some tall lax-eared European forms of T. vulgare and varieties of T. 

 durum and T. turgidum with slender straw exhibit this drooping habit in a 

 slight degree, and are correspondingly liable to go down under conditions 

 of weather which would not damage the stiffer erect straws of many 

 European winter wheats. 



The peculiar arrangement of the root-system and the strength of the 

 individual roots, which are hereditary characters of different varieties of 

 wheat, have a great influence upon the " lodging " of the crop. 



In short-strawed win- 

 ter wheats of the Square- 

 head type the bases of 

 the straws just above the 

 ground bend outwards in 

 the form of a cup, and 

 from their lower nodes 

 arises a spreading system 

 of adventitious roots (B, 

 Fig. 67) ; the first inch 

 or two of the roots below 

 the surface is somewhat 

 rigid and thickened con- 

 siderably, and the cell 

 walls of their tissues 

 strongly lignified. By this 

 spreading arrangement of 

 strong roots the plants 

 are firmly anchored to 

 the soil and prevented 

 from being laid except by 

 the severest storms. 



In most spring forms, 

 however, the straws grow 

 up from the ground in a crowded more or less compact bundle, spreading 

 very little, and the adventitious root-system consists of much thinner, less 

 lignified roots closely contracted and descending almost vertically with 

 very little grip on the surface soil (A, Fig. 67) ; plants with these root char- 

 acters are very easily bent to the ground as a whole, although the straw 

 may be as strong and rigid as that of the best winter varieties. " Lodging " 

 of this kind, which may even occur among isolated well-grown plants, is due 

 to weak root-hold, the straw being neither bent nor broken ; it is frequently 

 observed among rapid-growing oriental wheats when grown at Reading. 



FIG. 67. A, Stems and roots of a " spring " wheat ; 

 B, a " winter " wheat. 



