8o THE WHEAT PLANT 



In addition to the hereditary characters of root and stem which in- 

 fluence the " lodging " of the crops, there are external factors which 

 encourage " lodging," and the phenomenon, as ordinarily encountered in 

 farm practice in this country, is most frequently associated with weakness 

 of the straw due to the crowding of the plants. The weakness is chiefly 

 an etiolation effect caused by insufficient light. In dense closely-grown 

 crops the retarding action of light on growth is absent ; lengthening of 

 the lower internodes and of their cells occurs, and thickening and lignifica- 

 tion of the mechanical tissues of the straw are greatly checked in dull light. 



By comparing normal straws, which have had ample space for develop- 

 ment and adequate exposure to light during growth, with those of closely 

 grown crops, it is found that the lower internodes of the latter are some- 

 what longer, their diameter smaller, and their tissues somewhat softer 

 than those of plants grown wider apart. The vascular bundles in straws 

 of the same order, both in crowded and uncrowded plants, are similar in 

 number, but their transverse sections and the cells of the hypodermal 

 tissue are slightly smaller and the cell walls thinner in straws of crowded 

 plants than in those of normally grown stems ; both the hypoderm and 

 mechanical tissue round the vascular bundles are reduced in weak stems, 

 and their individual cells comparatively small and thin-walled ; in the 

 weakest crowded straws, which are sometimes little more than 1-5-2 mm. 

 in diameter, the tissue outside the zone of vascular bundles up to the 

 epidermal layer consists of cells with delicate walls only. 



The strength of the straws of " unlodged " plants is chiefly due to 

 the thick lignified walls of the hypoderm. 



Crowding, which results in etiolation, to which the weakness of the 

 straw is due, may be brought about in many ways ; the sowing of too 

 much seed per acre, drilling in rows too close together, early sowing, 

 the application of large amounts of nitrogenous manures to the soil, a 

 mild winter with abundant rain, and other conditions which encourage 

 luxuriant growth may each produce it, and when several of these factors 

 work together " lodging " is almost certain to follow sooner or later. 



Large leafy plants when crowded together, whatever the cause of their 

 luxuriance, are not only liable to " lodge " because the lower internodes 

 are weakened by being shaded, but they go down more quickly than 

 smaller plants because of the greater weight of their leaves and ears. 



Experiments with various fertilisers on the wheat crop, carried on for 

 several seasons at the College Farm, showed that the application of 

 phosphatic and potassic fertilisers alone, even in very large doses, had 

 little or no effect on " lodging " ; on the other hand, plants grown with 

 large amounts of nitrates of sodium, potassium or calcium, and sulphate 

 of ammonia, invariably go down in crops of ordinary density because the 

 straw is weakened by the etiolation which occurs. 



