the Broad Bean and certain other Plants. 
639 
The remarkable feature, however, in this experiment, was the recovery 
of the plant subsequent to the addition of boric acid. In every case 
(except a few of those deprived of boron for sixty days), though withering 
had apparently taken a complete hold of the plant, some renewal of growth 
took place, whether it was merely the production of a few new roots, or the 
development of a large secondary shoot and an almost entirely new root system 
(PI. XIII, Figs. 3 and 4). It would seem, therefore, that boron is able to 
benefit the plant even at a late stage in its growth, though its effect is 
certainly less pronounced than when supplied before the injury due to its 
absence is too far advanced. 
(a) General type of recovery subsequent to the addition of boric acid. 
The individual history of one of the plants showing recovery is interesting 
and may be taken as typical of the majority of others (PI. XIII, Fig. 4). 
i. The plant was grown in normal solution for twenty days and then 
placed in a similar solution which contained 1 : 2,500,000 H 3 B 0 3 . 
ii. Four days later, signs of ‘dying off’ in the shoot were evident. 
(Possibly the preliminary stages of withering had been overlooked when 
the plant was transferred, or the disorganization may conceivably have 
already set in, though not have been visible.) 
iii. Fourteen days later the shoot was still very poor, but fresh growth 
was taking place in the root. The short, thick roots, typical of plants 
grown in the absence of boron, began to elongate into long, fine ones, and 
entirely new laterals were also produced. At an early stage in this renewal 
of growth, the line of demarcation between the old and new portion of the 
root was clearly defined, and presented a most curious appearance. 
iv. Nineteen days later, though the main shoot still remained withered, 
a healthy secondary shoot was in flower. Besides being considerably 
larger than the original shoot, this secondary branch was different in appear¬ 
ance from the main axis. The leaves were rather lighter in colour, thin and 
not leathery in texture, giving the whole shoot an almost succulent appear¬ 
ance. By this time the root system was composed of a dense mass of 
laterals, though formerly there had been only a few short and thickened 
roots. 
In some cases apparently healthy tillers were produced by plants grown 
without boron. At first sight, this appeared to be conflicting with the view 
that it was the presence of boric acid that caused the renewal of growth. 
However, such tillers never flowered, always remained stunted, and eventu¬ 
ally ‘ died off’ in a similar manner to the main axis. 
In a few isolated cases, another type of recovery took place. The 
plant did not show any definite signs of ‘ dying off ’ when transferred to the 
solution containing boric acid, although it had been grown for a very con¬ 
siderable time without boron and was in a poor condition. After thirty 
days’ treatment, a number of fresh green leaves were noticed at the apex of 
U u 
