96 RELATIONS OF FOLIAGE-LEAVES TO ABSORBENT ROOTS. 
wick. By means of both contrivances advantage is ensured in that the water 
only oozes quite gradually down the moistened grooves, or else is conducted by 
the hairy fringes to the base of the stem, and does not rebound at any spot in 
the form of drops. Irregularly bounding drops would be liable to fall on the 
ground at spots where no absorptive organs awaited them. 
In cases where foliage-leaves, adapted to a centripetal conduction of rain, are 
arranged upon a spiral line down the stem, instead of in pairs opposite one another, 
the water leaks away along the spiral from one leaf to the next, and finally to 
the bottom. Then, again, there are often grooves in the stem along which the 
water trickles, as, for instance, in the Common Whortleberry (Vacciniwm Myrtillus). 
The erect leaves of this plant conduct the drops as they fall to the branches, 
which are deeply furrowed. The water travels through the furrows into those 
of lower branches, and finally along those of the main stem of the whole bush 
down to the earth. In Veratrum albwm each of the concave cauline leaves has, 
on the upper surface, a number of deep longitudinal grooves, which all discharge 
together at the base of the leaf. The water collected there at length overflows 
and runs down the round stem in no particular channel. 
The descent of rain-water along a spiral line may be very clearly traced in 
many plants of the Thistle tribe. If tiny shot-grains are substituted for rain- 
drops in a stiff-leaved plant, the course designed for the drops in that particular 
species may be followed with ease. When strewn on a mature plant of the 
Safflower (Carthamus tinctorius) or of Alfredia cernua (fig. 141), the grains 
of shot roll down the somewhat channelled surface of the highest cauline leaf, 
which stands up obliquely, and dash against the stem. The latter is half encom- 
passed by the leaf-base, and the shot then roll over one of the basal lobes of 
the leaf and travel out of the range of that leaf, falling on to the middle of 
the one next below. For the amplexicaul foliar bases are so placed that each 
leaf has one of its basal lobes above a concave part of the next lower leaf. In 
precisely the same way the shot descend from the second leaf to the third, and 
so on until they reach the earth quite close to the stem. The descent reminds 
one of the game in which a little ball is made to roll along a spiral groove on 
to a board furnished with numbered holes. Rain-drops falling upon thistle-like 
plants of this kind naturally follow the same course as the shot. Only, the 
additional fact must be taken into account that not only the highest but all the 
leaves are adapted as receptacles for the rain as it falls, and that consequently 
the drops falling from leaf to leaf are augmented by new tributaries, and become 
greater and greater as they descend. 
A somewhat different method of water-conduction from that which occurs in 
the Safflower and in the nodding Alfredia is observed in the Milk Thistle 
(Silybum Marianum), in the Cotton Thistle (Onopordon), and in the Mullein 
(Verbascum phlomoides). The upper leaves, which have two semi-amplexicaul 
lobes, are as nearly erect as those of the Safflower and the nodding Alfredia, 
and lead the rain off in exactly the same way. But the leaves in the middle 
