8 
there a living root covered near its growing tip with root hairs. In 
the zone of the root where the root hairs occur these structures are 
remarkably abundant, the large majority of the epidermal cells of 
the root being developed into hair structures. It is a difficult matter, 
therefore, to wash the soil away from these portions of the roots 
without tearing off the root hairs. It is impossible to determine with 
certainty the causes which bring about the great variation in the 
length and number of living roots on plants which seem to be quite 
vigorous and on normal soils. The proper development of the root 
system, however, seems to depend largely upon suitable physical con- 
ditions in the soil. Where drainage is poor and where the soil 
becomes packed or puddled below the depth of cultivation, it is 
impossible for the roots to penetrate and develop as they otherwise 
might do. 
In general it may be said that the root system of pineapples grow- 
ing on highly manga niferous soils is rather less extensive than that 
observed on normal soils. The number of small fibrous branches on 
the main roots is much reduced in manganiferous soils. One of the 
most striking effects of a high percentage of manganese in the soil is 
observed in the root tips, which quite generally show rounded swollen 
ends rather than the pointed tips with rootcaps, such as occur in nor- 
mal soils. These swollen root tips are almost invariably dead or 
dying and usually are found in process of decay. It is obvious that 
they have in all cases ceased growing. In fact, growth is impossible 
after the swelling occurs, since the roots are then unable to penetrate 
farther into the soil. In the woody tissue and in the cells imme- 
diately under the epidermis of roots growing in manganiferous soil 
there is a slightly greater tendency toward browning of the cell walls 
than is the case in normal soils. 
LEAVES. 
The leaves of the pineapple and other members of the same family 
with similar habits of growth are attached to the short stems of the 
plant close together and spread at an angle of 45°, more or less, from 
the axis of the plant. The edges of the leaves are curved upward, 
so that a cross section of a leaf is approximately a semicircle. 
In the normal pineapple plant the upper surface of the leaf shows 
a conspicuous red color, which is confined to the central third of the 
leaf surface. The upward curving of the edges of the leaf naturally 
divides the upper surface of the leaf into three nearly equal portions, 
two being upright, one on either side, and the third portion lying at 
the bottom of the trough. This central or lower third receives the 
sunlight to a much greater degree than the sides of the leaf, and the 
development of a red coloring matter in the lower third seems to be 
[Bull. 23] 
