82 TRACE ELEMENT DEFICIENCY 



bring about cessation of cell division in the root apex and 

 degeneration of the root cap. In rutabaga the thin- walled cells 

 of the meristematic tissue of the stem apex and of the root 

 cortex became crushed, while cells near the cambium became 

 elongated and the cork cambium failed to produce cork. In 

 cabbage Jolivette and Walker recorded considerable prolifera- 

 tion of cells in the cambial region resulting in a zone of meri- 

 stematic tissue between xylem and phloem several times the 

 usual width of this band, while there was a corresponding reduc- 

 tion in the amount of differentiated xylem and phloem. In 

 radish Skok found that vascular tissue near the axis which 

 might have been produced while boron from the seed was still 

 available, or from boron present as impurity in the substrate or 

 chemicals used, was usual, but that there was a complete absence 

 of normally developed and lignified xylem vessels in the region 

 between this inner tissue and the cambium, while the later 

 formed phloem disintegrated. Xylem parenchyma cells, al- 

 though smaller than normal, appeared uninjured. Owing to the 

 failure of the development of normal vascular tissue the roots 

 cracked and then the cambium and phloem mostly disintegrated. 

 In swede, according to Jamalainen, the first symptom of boron 

 deficiency is enlargement of xylem parenchyma. 



In the squash Alexander noticed that boron deficiency 

 brought about hypertrophy and collapse of the meristematic 

 cells and of more mature cortical cells of the apical region of the 

 stem, while, towards the apex of the root, cells of the central 

 cylinder were similarly affected. In older regions of the stem 

 parenchyma of the ground tissue, xylem, and the region be- 

 tween xylem and internal phloem showed abnormal enlargement. 

 Cells of the cambium were also enlarged. Enlargement of thin- 

 walled cells also occurred in the leaves. 



In garden beet the first internal symptom, according to 

 Jolivette and Walker, appears in the phloem where certain cells 

 resembling companion cells become filled with a densely staining 

 substance. Occasional hypertrophy of cambial cells was also 

 noted. Later degeneration of xylem tissue occurs. 



The first internal deficiency symptom of maize was found 

 by Eltinge to be a disintegration of some of the leaf cells. 

 Later, entire cross-sections of a leaf might collapse, and in other 



