96 JiELATIOXS OF FOLIAGE-LEAVES TO ABSORBENT ROOTS. 



wick. By means of botli contrivances advantage is ensured in that tlie water 

 only oozes quite gradually down the moistened groove.s, or else is conducted bj* 

 the hairy fringes to the liase of tlie stem, and does not rel>ound at any spot in 

 the form of drops. Irregularly hounding drops would be liable to fall on the 

 gi'ound at spots where no absorptive organs awaited them. 



In cases where foliage-leaves, adapted to a centripetal conduction of rain, ai-e 

 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 {Vaccinm'ni Myrtillus). 

 The erect leaves of this plant conduct the dro|^)s 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 Veratricm album each of the concave cauline leaves lias, 

 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 verj'' clearlj^ traced in 

 many plants of the Thistle tribe. If tiny shot-grains are substituted for rain- 

 drops in a stifl-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 

 Saffiower (Carthamus tinctorius) or of Alfredia cerniia (fig. 14^), 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 nest 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 thiixl, 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 I'ain 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 Saffiower and in the nodding Alfredia is observed in the Milk Thistle 

 (Silybtim Mariamom), in the Cotton Tliistle {Oncrpordon), and in the Mullein 

 {Verhascwiii phlomoides). The upper leaves, which have two semi-amplexieaul 

 lobes, are as nearly erect as those of the Saffiower and the nodding Alfredia, 

 and lead the rain off in exactly the same way. But the leaves in the middle 



