20 BORTHWICK-—ADVENTITIOUS ROOTS AND RELATION 
few cases did the phellogen show any unusual activity. Again, in 
all cases I found a connection between the cambium of the stem 
and that of the root—a fact which is not figured or mentioned 
by the above authors in the species examined by them. 
Geyler! has shown that the production of aerial roots is a 
common occurrence on Laurus canariensis. Their time of vege- 
tation lasts from the end of autumn to the beginning of summer 
in the following year, when they turn blackish, dry up, and fall 
off. They occur at varying heights on the stem and are especi- 
ally abundant near branch-wounds, around which they occur in 
circles. They seem to occur more abundantly in moist, shady 
gullies where many laurel-trees are thickly crowded together, 
while they are not to be found on single standing or isolated 
trees. The author ascribes their formation to the action of a 
parasitic fungus, and it would seem that here the production of 
aerial roots is purely pathological. 
Lawson’s Cypress and Thuja gigantea. 
There are many specimens of Cupressus Lawsoniana and Thuja 
gigantea in the Royal Botanic Garden which show numerous 
papilla-like projections standing out at right angles to the shoot- 
i ese are frequently of a bright green colour and vary in 
shape from that of a cone to that of a sphere. They seldom 
exceed 3mm. in length or diameter ; they may occur all over the 
shoot, on the leafy twigs as well as on older shoots from which 
the leaves have fallen. Externally they appear merely as raised 
portions of the periderm and are irregularly distributed all over 
the shoot-axis (Plate VIII., Fig. 12). 
If a section is made so as to pass either in a transverse Or ina 
radial longitudinal direction through the stem-axis, the protuber- 
ance is seen to be in organic connection with the wood-body of 
the mother-stem. Such sections are shown in Plate VIII., Figs. 4 
and 5, in both of which it is clear that the wood-cambium of the 
stem passes into the outgrowth and further, that in the out- 
growth two distinct regions may be recognised—a central axile 
portion and a peripheral cortical one. It will also be seen that 
the cortex of the stem takes no part in the formation of the 
papilla, but that it is merely passively stretched. 
1H, Th. Geyler, in Bot. Zeit., Vol. XXXII (1874), p- 322. 
