Root Development in Aluminous Soils— Plucknett, Moomaw, and LAMOUREUX 
403 
Root: Development of Leucaena glauca 
•Root development of Leucaena glauca in 
treated subsoils of the Halii and Kapaa soil 
series was investigated separately in pots. In 
both the Kapaa and Halii subsoils root develop- 
ment was usually restricted to the untreated top- 
soil if subsoils were untreated. The greatest root 
development in subsoils was produced by P 
treatments. Treatments in which lime was added 
in addition to P stimulated root growth more 
than lime alone. The addition of 1,000 lb of ele- 
mental P without lime produced the most root 
penetration into the subsoils and also the 
highest plant yields. 
Comparative root systems produced by treat- 
ments in the Kapaa subsoil are illustrated in 
Figure 4. Tap roots of L. glauca in the P treat- 
ments were straight and penetrated to the bot- 
tom of the pot. Tap roots of check plants did not 
develop in the untreated subsoils. The effect of 
treatment on tap-root penetration and root de- 
velopment in treated Kapaa subsoil ranked as 
follows: P > lime plus P > lime > check. 
Figure 5 shows comparative root systems in 
Halii subsoils. Roots of check plants in the 
Halii subsoils penetrated slightly into the sub- 
soil, but total root development in the check was 
much less than total development in subsoils 
treated with P and with lime plus P. 
Two types of tap-root development with 
treatment were observed: A long straight tap 
root was characteristic of P treatment, while a 
Fig. 4. Plants of Leucaena glauca grown in treated 
subsoils of the Kapaa series. Treatments from left to 
right are: 500 lb P, 1,000 lb P. 5 tons lime, 5 tons 
lime plus 1,000 lb P, and check. 
Fig. 5. Plants of Leucaena glauca grown in treated 
subsoils of the Halii series. Treatments from left to 
right are: check, 5 tons lime plus 1,000 lb P, 5 tons 
lime, and 1,000 lb P. 
branching tap root was characteristic of the 
lime plus P treatment. 
An interesting result of treatments added to 
Halii subsoils was the number of nodules pro- 
duced on roots of L. glauca. Most nodulation 
occurred with lime plus P, but lime alone also 
stimulated nodule formation. Only one nodule 
was found with P treatment, and no nodules 
were found in the check. 
Staining of Leucaena glauca Root Tips 
Hematoxylin staining of cell walls, nuclei, and 
cytoplasm was evident (Fig. 6d) . Outer walls of 
epidermal cells were especially heavily stained 
( Fig. 6a, b) , which may indicate a precipitation 
of aluminum in this region. In P- treated plants 
two darkly stained areas at the periphery of the 
stele were observed, which may also represent 
areas of aluminum precipitation. One of these 
areas is shown in Figure 6c. The cells of the 
stele appeared to stain more intensely than those 
of the cortex (Fig. 6a, b), but the stelar cells 
are less highly vacuolated and thus contain 
more stainable material per unit volume than 
the cortical cells. 
Staining was more intense in roots from the 
check (Fig. 6a) than in roots from lime-treated 
soils (Fig. 6b). Phosphate-treated roots stained 
more heavily than Jime-treated roots. Roots 
treated with a combination of 5 tons lime 
plus 1,000 lb P stained more deeply than those 
treated with lime alone, but in most cases 
