45 8 Harvey-Gibson. — Contributions to Knowledge of 
orientation, so that the concave faces of the branch-bundles 
oppose each other. This alteration of the axis of the bundles 
has already been pointed out by several observers and seems 
to be a general rule for the genus. Unicellular root-hairs 
occur right up to the caps of the young roots. 
Although there are some slight individual differences in 
the structure of the cortex, the development of the endodermis 
and in the amount of extension of the protoxylem, the 
structure just described for S. atroviridis holds good for the 
great majority of the species I have examined. There are, 
however, a few points of interest which may now be alluded to. 
Approaching quite closely to the type are the roots of 
S. plumosa , Bale., vS*. Martensii , Spr., X. Douglasii , Spr., 
*S. serpens , Spr., 5. apus , Spr., S', convoluta , Spr., S. albonitens , 
Spr., S. jiabellata , Spr., S. producta , Bak., S. bisidcata , Spr., 
S. concinna , Spr., S. uncinata , Spr., S. molliceps , Spr., S. Vo- 
gelii , Spr., S. patula, Spr., S. haematodes , Spr., S. Karsteniana , 
A. Br., S. grandis> Moore, S. erythropus , Spr., S. Braunii , Bak., 
S. pilifera , A. Br., S. viticulosa , Klotz., and S.caulescens , Spr. 
In this last-named species the cortex is very sclerotic, and 
the endodermis becomes greatly thickened towards the peri- 
cycle. Both pericycle and phloem-parenchyma may become 
sclerotic in very old roots. 
In S. involvens , Spr., the roots arise from the bases of 
the closely growing stems and enter the ground at once. 
Anatomically the root is peculiar as regards its cortex. 
Superficially there is a layer of cubical cells, each of which 
gives off a root-hair. This layer is followed by a layer of 
large cells ovoid in section and very regularly placed, and 
that by a small-celled cortex, small-celled outwardly but 
becoming larger inwards, and bounded internally by a well- 
marked endodermis. The vascular cord is normally monarch. 
vS. cuspidata , Lk., and S. lepidophylla , Spr., agree in all points 
of structure with 5. involvens (PI. XX, Fig. 5 ). All the above- 
mentioned species are monostelic so far as their stem-structure 
is concerned. There are two other species, both belonging 
to the monostelic type, which exhibit a somewhat peculiar 
