226 J. H. Priestley and R. M. Tupper-Carey 
in water upon the growth of a root system, than the impossibility 
of absorption by this region. There is considerable evidence, often 
unwillingly obtained in water cultures, that with many plants, the 
growth of the root system thus immersed is less satisfactory than 
usual whatever may be the cause. This is particularly true of some 
of the plants with which Coupin records positive results, notably 
peas and beans. In the case of plants growing with their root apices 
inserted by a watertight join into a glass tube containing moist air 
it is very difficult to be sure that the experimental conditions have 
not been obtained at the cost of such damage to the root apex as 
will prevent further growth. 
It is possible to demonstrate experimentally that roots will 
grow when completely out of water. Germinating seeds of Vida 
Fab a L. were taken immediately after the roots had burst through 
the testa and grown in bottles in the dry air of the laboratory, the 
necessary water being supplied only through the cotyledons. The 
roots continued to grow and, although sturdier than usual, attained 
a length of two or three inches before the outgrowth of the plumules 
rendered it difficult to continue to supply water to the cotyledons 
without leakage. It was noticeable that when compared with roots 
grown in damp sawdust, these roots in dry air produced lateral 
rootlets more slowly. In the earlier experiments the upper portions 
of the cotyledons were cemented by plaster of Paris into a wide 
glass tube, but the continual swelling of the bean broke the plaster 
of Paris, so that the water leaked on to the root. In later experi¬ 
ments the beans were fixed in position by plasticine made water¬ 
tight by a layer of 20 per cent, gelatin; the bean growing as shown 
in text-fig. 2. These roots were very striking structures, clothed to 
within a short distance of the tip with a coat of short hairs, sturdier, 
more numerous and persistent than the usual root hairs. These 
experiments effectually dispose of Coupin’s contention that the root 
will not grow if the apex is out of water, the roots having grown with 
their whole length in dry air since they had attained a length of a 
few millimetres. 
From a comparison of growth of seedlings with their root tips 
in distilled water or in Knop's solution, Coupin ( 5 ) has attempted to 
show that salts in solution also enter the plant by the root 
apex. 
But if the water film is drawn up by surface tension to the cor¬ 
tical absorptive region of the root, the salts in solution will be drawn 
up with it and may enter the root without necessarily passing 
