34 BORTHWICK—ADVENTITIOUS ROOTS AND RELATION 
root or shoot, because the potentiality of producing either 
certainly resides in the medullary ray. 
The conditions which govern the production of the adventi- 
tious roots have, so far as I know, not yet been determined. 
Certainly moisture plays a very important role in their subse- 
quent development, as it is only in the moistest situation that 
they persist for any time after aig pierce the periderm. This 
was very well marked in Twa 
Conclusions. 
1. The medullary rays of Cupressus Lawsoniana, Thuja 
gigantea, Cupressus pisifera, Cupressus pisifera plumosa, Acer, 
apple, and elm may become broad and cylindrical and be con- 
tinued out into adventitious roots. 
2. Such abnormal medullary rays and adventitious roots may 
be produced abundantly on the burrs found on elm and mountain- 
3. Those adventitious roots may cause, like adventitious buds, 
-bird’s-eye formation in wood. 
4. In none of the above cases, except possibly the cherry- 
laurel, did the formation of these adventitious structures appear 
to be the result of mechanical injury, fungus, or insect attack. 
I have to express my indebtedness to the Regius Keeper for 
much valuable advice and the many facilities afforded to me 
while engaged in carrying out the investigations of which the 
above is a record. 
Explanation of the Figures in Plates VIII.-XI. 
PLATE VIII. 
Fic. 1.—Willow tree trunk, bearing numerous adventitious roots. 
Fic. 2.—Gean tree stem, with swollen base ciate. numerous adventi- 
tious roots. 
Fic. 3.-- Gean tree, piece of bark cut from the stem at a height of several 
feet from the ground, showing cluster of adventitious roots. 
FIGS. 4-12.—Cupressus Lawsoniana. 
Fic. 4.—Section transverse to stem and longitudinal to adventitious root. 
