98 RELATIONS OF FOLIAGE-LEAVES TO ABSORBENT ROOTS. 



a source of nutriment to the absorption -roots which proceed from it. In the 

 Milk Thistle (Silybum Marianum) the margins of the cauline leaves are very 

 much waved, and, in consequence of this undulation, three or four depressions exist 

 on each side, through which part of the rain, when there is a heavy downpour, 

 flows off sideways. But even this water, falling laterally, drops upon parts of 

 lower leaves, which conduct centripetally, and so coalesces with the streamlets 

 otherwise produced. 



It is very rare for plants which convey water centripetally to have their leaves 

 arranged in two rows. The most striking example of this class is the Japanese 

 Tricyrtis pilosa. Its leaves are situated on the fully -developed stem very regularly, 

 one above the other, in two series. Each leaf has two lobes embracing the stem, 

 but the base is fixed somewhat obliquely, so that one of the lobes is fixed higher 

 than the other. Moreover, the higher lobe is closely adpressed to the stem, whilst 

 the lower forms a channel which discharges exactly above the concave surface of 

 the next lower leaf belonging to the other side. When rain falls on this plant, 

 the water, collected by one leaf, flows through the broad exit-channel on to the 

 leaf below on the other side. Thence a somewhat augmented stream falls upon 

 a leaf of the first series, and so on, a peculiar cascade resulting, which falls in 

 a zigzag, from leaf to leaf, until it reaches the bottom, close to the stem. 



It would, however, be wrong to suppose that the above explanation sets forth 

 the only significance to be assigned to the various arrangements described. To 

 many plants it is a matter of indifference in what direction rain-water falls from 

 the leaves. Such, for instance, is the case with all marsh -plants with roots 

 buried in mud under water, inasmuch as the rain, as it drops, only goes into the 

 water in the pond or marsh, and could not be conveyed to a definite spot for 

 the sake of the absorbent roots. In the Water-plantain, the Flowering-rush, and 

 the Arrow-head (Alisma, Butomus, Sagittaria), accordingly, no relationship between 

 the form and direction of the leaves and the position of the absorbent roots is 

 to be discovered. 



On the other hand, in arundinaceous plants (Arundo, Phragmites, Phalaris) 

 an arrangement has been hit upon which is obviously designed to prevent rain- 

 water from collecting between the haulm and the leaf. As is the general rule 

 with grasses, so also in the above-named kinds of reeds, the stem or haulm is 

 furnished with nodes, and from each node proceeds a leaf the lower part of which 

 encases the haulm in the form of a tube or sheath, whilst the upper part is expanded 

 and presents a flat, strap-shaped or concave surface, standing well away from 

 the stem. The leaves may be folded round the haulm like banners. At the place 

 where the sheath passes into the part of the leaf which stands away from the 

 axis at an obtuse angle, one observes on the edge of the leaf close to the angle, 

 two distinct depressions which represent conduits and convey part of the rain from 

 the lamina. There is also a very neat contrivance here in the form of an erect dry 

 membrane which acts as a dam, the so-called " ligule." This membrane, inserted 

 upon the leaf -sheath, is, like the sheath, in contact with the haulm. When rain- 



