32 BORTHWICK—ADVENTITIOUS ROOTS AND RELATION 
In addition to this specimen there are two wych elms (U/mus 
montana), not far from the palm-house, which bear at their bases 
the large burrs so characteristic on many trees of this species. 
Numerous water-shoots have sprung up round their bases, form- 
ing a thick cover. These water-shoots all bear well-developed 
protuberances, especially on their under side, which resemble in 
appearance and agree in structure with those seen in Plate XI, 
Figs. 44 and 45. However, those adventitious roots were not 
confined to the branches alone, but were also to be found 
scattered over the surface of the burrs, which were, as usual, 
thickly covered with small adventitious shoot-buds, nevertheless 
a careful examination showed that many root-rudiments which 
might have been easily passed over for buds were also present: 
The size and shape of both structures were fairly similar, but the 
absence of bud-scales soon led to the detection of the root- 
rudiments which sometimes, though rarely, grow out into aerial 
roots. (See Plate XI., Fig. 48, which is a piece cut out of one of 
the burrs.) A radial longitudinal section of a bud (Plate XI. 
Fig. 48), and of a root-rudiment (Plate XI., Fig. 47), show dis- 
tinctly the characteristic differences between those structures. 
The two specimens seen in these two figures were picked off a 
burr on which they were growing side by side. 
Mountain-Ash. 
Quite recently I came across the same phenomenon in a 
mountain-ash (Pyrus Aucuparia), which bore several large burrs 
near the base of its stem. The adventitious roots produced on the 
burr in this specimen were large, well developed, and abundant. 
Cross sections of the burrs (of both elm and mountain-ash) 
show that the inward prolongations of these roots cause the 
vascular tissues to assume a very irregular course. In fact the 
effect of these adventitious roots on the vascular tissues of the 
burr is very much the same as that of the adventitious buds 
described by Professor Marshall Ward.} 
Cherry-Laurel. 
There yet remains to be mentioned the occurrence of those 
adventitious roots in the cherry-laurel. 
*Marshall Ward, Disease in Plants (1901), p. 224. 
