94 RELATIONS OF FOLIAGE-LEAVES TO ABSORBENT ROOTS. 
bulbs or short root-stocks with deep-reaching suction-roots, and those which have 
tap-roots descending vertically in continuation of the main stem, and whose second- 
ary roots are short and travel only a little distance from their places of origin. 
This other extreme in root-structure, which is represented in fig. 137, has its 
counterpart above-ground in the form and direction of the laminze upon which 
the rain falls. In all these plants the surfaces of the leaves are not directed 
Fig. 13.—Centrifugal and Centripetal Transmission of Water. 
1By a Caladium, * By a Rhubarb plant. 
outwards, but slope obliquely towards the central axis. Their upper sides, more- 
over, are concave and exhibit a system of grooves, which conveys the water collected 
by the leaf towards the stem, and therefore also, towards the tap-root and suction- 
roots. The leaves of bulbous plants, such as the Hyacinth and Tulip, all stand 
up obliquely, and their upper surfaces are concave and often deeply channelled. 
Along the grooves the rain flows centripetally downwards, and so directly reaches 
the part of the earth where the bulbs and suction-roots, which proceed in a tuft 
from underneath the bulbs, are situated. The young leaves of Cannacew and of the 
Lily-of-the-valley are coiled up like a trumpet; and rain, falling from above 
upon the expanded portion, is led along the coiled surface, describing a helix as 
