THE ROOT-SYSTEM OF IMPATIENS ROYLEI. 495 
the ground-level between the four roots already there, or they may occur at 
any point slightly higher on the hypocotyl. The subterranean adventitious 
roots show a like freedom in development. 
Both aerial and subterranean adventitious roots are much stouter than the 
primary laterals, and they characteristically possess a bluntly rounded apex 
when they emerge from the stem. The aerial ones develop a red epidermal 
pigment, similar to that oceurring in the epidermis of the stem, and they 
sometimes show а rather sudden decrease in diameter about two-thirds of 
the way from the base to the tip (text-fig. 18 0). Round the base of each 
root is a projecting rim formed by the tissue of the axis (text-fig. 2). 
D. On the main avis of upright plants. 
In perfectly upright uninjured plants many adventitious roots arise near 
the ground-level; they develop lateral roots freely upon entering the soil 
and grow to a considerable length, thus forming a large accessory root- 
system, but they rarely occur in any numbers at higher points on the hypo- 
cotyl, and in only one case have they been found to appear on the main axis 
above the first (7 е., the cotyledonary) node. In this exceptional case (text- 
fig. 3) four stout roots grew out at the base of the first epicotyledonary 
internode, and were nearly equally spaced round the stem, but in spite of 
their early promise they soon ceased growing and never reached the soil. 
In this respect they resembled the solitary adventitious roots on the upper 
portion of the hypocotyl. 
С. On lateral branches. 
Although it is exceptional in upright plants for adventitious roots to 
develop normally on the main axis above the first node, they are produced in 
large numbers from the lower side of the swollen bases of the robust lateral 
branches (text-fig. 4a). In the largest plants (height two to three metres) 
they occur as high as the fourth branch whorl from the base, but the roots 
decrease in frequency from below upwards, and are never produced from 
feeble branches. The swollen base of one branch may bear as many as ten 
roots, and in all cases the roots, where at all numerous, are closely crowded. 
It is in these roots that the typical narrowing, one-third distant from the tip, 
is most frequently shown. | No roots developed from lateral branches exceed 
a length of three or four centimetres, and they are, therefore, normally 
abortive. 
D. In plants bent at the nodes. 
In large beds of closely crowded plants upright specimens are exceptional. 
Not only do the weakly and injured plants trail for some distance along the 
ground, but those that are comparatively well developed, with a height of 
one and two-third metres, and a basal diameter of two to three centimetres, 
show a bend at the first node, so that the hypocotyl makes an acute angle 
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