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been able to analyze. A recent paper by Bennett? shows that many cases, at 
least, of apparent aérotropism are really hydrotropic, and the same is probably 
true with the Cocos, The roots maintain a deeper level in sand than in heavy 
soil. When the other stimuli are removed, a variable geotropism shows itself; 
some, in water, grow straight ahead in as nearly horizontal a direction as it was 
convenient to arrange them in the bottle; but the majority show a feeble positive 
geotropism, the most rapidly executed curve being 40° in two days. The second- 
ary roots are usually controlled by their autotropism alone. In heavy soil they 
are sometimes more numerous on the upper sides of the main roots, probably 
because of an induced geoauxesis, since the structure of the roots precludes the 
probability of any direct locative influence of moisture on their origin, and the 
pneumathode roots appear on all sides. In nature, no roots will grow to any 
distance into water, nor into a level of the soil where water stands; and a rise 
in the water level ultimately kills the submerged ones. 
foot structures.—The stelar tissues of the coconut root offer very little 
that needs description. The number of xylem rays is usually 40 or more 
in the larger, 10 to 15 in the branch roots, 1 to 1.5 millimeters in dia- 
meter, and fewer in the finer ones. In the young parts of the main 
ones the pith is parenchymatous, with very thin walls. The latter begin 
to thicken at a distance from the apex at which both hypodermis and 
endodermis have reached their permanent state. They then become very 
thick throughout, and are the chief source of the root’s great tensile 
strength. 
In cross sections, a very few cells behind the growing point, the pericycle 
is distinguishable by the regularity and the large size of its cells. The 
latter eventually become somewhat flattened tangentially, but they still 
form a conspicuous layer in sections of old roots, as their walls remain 
thin and colorless. The cross partitions are reticulate-punctured. . 
In very young parts of the root the endodermis can be identified only 
by reference to the pericycle (fig. 2). Its cells begin to thicken at about 
the same point as do those of the hypodermis, where the latter begins to 
interfere with the absorption of water. The thickening takes place cell 
by cell, rather abruptly in the individual cells, but without any uniform- 
ity throughout the layer, so that in some sections a few will be found 
well thickened, all the others still thin; while a little farther back most 
of them will be found to be thick. Counting all the endodermal cells in 
a section, an undue proportion of those which thicken late is directly 
outside the xylem rays, where passage cells would be expected. However, 
cells in this position are not infrequently among the first to thicken, 
whereas scattered ones found elsewhere are often among the last. Con- 
sidering the zone with reference to the hypodermis at which the thicken- 
ing of the endodermis begins, it is evident that it is only as the water 
travels obliquely up the root to the stele, and not directly inward, that 
any of the cells remaining thin have occasion to serve in its passage. The 
appearance of the old endodermis is shown in the accompanying figure 
(fig. 1). . 
* Bot. Gaz. (1904), 37, 241, 
