122 THE FUNCTIONS OF 



indicated in the work of Johnston and Dore (1929), who found 

 that in tomato plants suffering from boron deficiency there was 

 a marked accumulation of sugars in the leaves and a corre- 

 sponding reduction of the sugar content of the stems, indicating 

 some considerable reduction below normal in the translocation 

 of carbohydrates. 



The work of Wadleigh and Shive (1939) on cotton seedlings 

 is also important in this connexion. They examined the effects 

 of boron deficiency in the seedlings by means of microchemical 

 tests. For this purpose seedlings were grown in water cultures 

 with and without a supply of boron. The first internal symptom 

 observed was the increased acidity of a few cells scattered 

 through the pith and cortex, the pH of these cells being from 3-8 

 to 4-4 as compared with the normal value of 5-8 to 6-4. As boron 

 deficiency increased so did the number of these abnormally acid 

 cells, which then also appeared in the pericycle and the older 

 xylem parenchyma. When the majority of the cells of the pith 

 had become very acid their cell walls began to break down, at 

 the same time developing a deep brown colour. Next, some of 

 the cells of the phloem and younger xylem parenchyma developed 

 high acidity and ultimately a breakdown of cells occurred in 

 these regions also. 



While these changes were proceeding accumulation of sugars 

 was observed in the boron-deficient plants, while starch was 

 abnormally abundant in the endodermis. In the cells of the 

 stem apices the nitrate-nitrogen content was much lower in 

 boron-deficient than in normal plants. This was attributed to 

 failure of nitrate absorption owing to death of the root apices. 

 There was a very marked accumulation of ammonia nitrogen 

 in the cells which develop high acidity. Wadleigh and Shive 

 conclude from the fact that both sugars and ammonia nitrogen 

 accumulate in boron-deficient plants that boron deficiency 

 brings about a decreased rate of oxidation of sugars, and of 

 amination of carbohydrate derivatives so that protein sub- 

 stances necessary for maintenance of protoplasm are not formed. 

 Microchemical tests for proteins supported this view, for Millon's 

 reagent, the xanthoproteic test and the biuret test all gave 

 immediate results with the abnormally acid cells of boron- 

 deficient plants, whereas in normal plants pre- treatment with 



