THE ROOT-SYSTEM OF IMPATIENS ROYLEI. 497 
direct rays of the sun owing to the shade cast Бу the wall, exhibited this 
feature markedly. The bending in all cases was away from the wall and 
towards an open space; it was also most marked where ihe shade was 
greatest and the plants most crowded and least robust. The pronounced bend- 
ing appeared, therefore, to be due to a combination of two factors, one of 
mechanical inefficiency, and the second of light stimulus ; the latter largely 
determined the direction of the bending. 
Fra. 4 ).— Diagram of transverse section of stem to show relationship of tissues. The xylem 
is represented as black areas, the phloem as a thin line. Т., adventitious roots ; 
fis., fistular cavity. 
p 
LN 
4c 
Ета. 4 c.—4A portion of 4 b enlarged to show detail; phloem dotted. 
When an inclination takes place, adventitious roots develop immediately 
above the cotyledonary node on the side nearer the ground (PI. 38. fig. 9). 
One or two may develop just below the node, but this is exceptional. The 
roots appear even where the deviation from the vertical is very slight, but 
when the hypocotyl is long they are generally abortive. In the majority of 
cases, however, the bending, when it takes place at all, is sufficiently marked 
for the roots to reach the ground after two or three centimetres growth. 
Upon entering the soil they produce lateral roots and often attain a con- 
siderable length (text-fig. 5). Thus the plant is fastened securely to the 
