458 The Botanical Gazette. [December, e 
especially be observed that the older the plant, the deeper — 
the base of the rootstock will penetrate, and the broader it — 
will become as a rule and hence the greater will be the direct 
resistance to be overcome. In many cases amore or lessde- — 
finite portion of the base of the rootstock dies every year. In — 
that event the remaining portion of the rootstock must pass — 
also through the space left by the decayed part, before it can 
sink its base to a still lower level. 
It is difficult to understand how the broad _base of a thick 
rootstock such as that of Agave Virginica L., for instance, 
or other still more striking instances, penetrate the har 4 
ground. One thing I have noticed is that plants of this de- — 
scription usually have good stout vertical roots from yeat to 
year, and that these begin to wrinkle transversely towards | 
the close of the season. Having a very good grip on the — 
ground by means of the minor rootlets, the tension they ite 
ert on the rootstocks by their contraction in length must t Ss 
enormous, but so must also be the resistance of the earth é 
below the rootstocks. The only plausible explanation there- ; 
fore seems to be, that the base of the rootstocks are 0 i ; 
force a passage slowly, little by little, when the grous Ne 
much softened by rains. | This is a subject needing more ©” 
the reverse process takes place. 
end of the rootstock is here direetas ee 
growth is formed along the rootstock deeper 1 ‘rectly 
that a considerable di of the rootstock 1s pointed pre 
downwards, earthward, increasing in size 1n a 
tion. At the lower thickened end, the tip of 
however bent abruptly to one side and tees d to the 
itself points upwards. Strong roots are attached to | 
rootstock and strong roots are also sent ‘ hat this curved 
scribed strong bend below. It is evident tha 
portion straightens itself out at intervals, 
the successively newer and straightened po ion 
the soil. In this way the base of the curved P evel 
rootstock behind the tip is sometimes found ge soil, from 
siderably more than a foot beneath the level of #26” . 
which level the rootstock must have started. : 
