Effect of Boron Compounds 67 



From the foregoing results it is evident that boron is very widespread 

 in the vegetable kingdom, entering into the composition of many plants 

 in all the great classes. A general impression obtains that its distri- 

 bution is universal, and that it will ultimately prove to enter into the 

 composition of practically every plant, as the scope of the analyses is 

 widened and as methods of detection are improved. On the other hand, 

 Agulhon is inclined to think that boron may be a " particular element," 

 characteristic of certain groups of individuals or of life under certain 

 conditions. The series of individuals differ among themselves as to their 

 particular needs of nutriment (in the widest sense) and doubtless each 

 group has special need of particular elements, a need that is possibly 

 correlated with morphological and chemical differences. It may well be 

 that boron is one of these elements, associated with certain vital functions 

 in a way as yet unexplained, though it may possibly be found to play 

 some part in the formation of vascular tissues, since it is most abundant 

 in bark and lignified parts. 



II. EFFECT OF BORON ON THE GROWTH OF HIGHER PLANTS. 

 1. Toxic effect. 



(a) Toxic action of boron compounds in water cultures. 



Excessive quantities of boric acid are decidedly poisonous to plants, 

 the action being well marked in water cultures. Knop (1884) found 

 that free boric acid was poisonous in neutral food solutions when 

 present at the rate of *5 gram per litre, but he was not able to detect 

 boron in the ash of the roots of the experimental plants. Archangeli 

 (1885) placed seedlings of maize, white lupins, Vicia sativa and Triti- 

 cum vulgar -e in solutions of boric acid varying in concentration from 

 1 "05 %, with controls in spring water. In the latter case the develop- 

 ment was normal, with 1 % boric acid the plants were killed, while it 

 was found that the weaker the solution (within the indicated limits) the 

 stronger the root and shoot growth. 



Hotter (1890) stated that it was known that 1/20,000 boric acid by 

 weight was harmful to soy beans in nutritive solutions. He experimented 

 with peas and maize, placing the seedlings first in distilled water, later 

 in nutritive solutions. When the peas were nineteen days old they 

 were transferred to nutritive solutions containing 1/1000 1/100,000 

 boric acid by weight per litre, and within three days the plants with 

 1/1000 showed signs of injury. Two days later all the plants showed 



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