THE DESCENDING SAP 



153 



say, an Oak or Elm growth below the 

 ring has almost immediately ceased, 

 conclusively showing that the flow of 

 assimilated nutrient sap to that part of 

 the stem has also ceased, and therefore 

 that the way of the sap's descent is the 

 bark. A branch of an ordinary fruit-tree 

 may be made to bear specially fine fruit 

 simply by binding it tightly with a ring of 

 stout wire ; for by this means the down- 

 ward flow of elaborated sap is checked, 

 and the fruit gets the benefit of all the 

 food produced by the leaves of the branch. 

 The fact is well known to gardeners, and 

 much of the prize fruit shown at exhibi- 

 tions is produced in this way. The upward 

 flow of crude sap of course goes on with- 

 out interruption through the uninjured 

 wood-vessels ; and thus the leaves above 

 the ring are duly supplied with raw 

 material from the soil, out of which to 

 elaborate new descending sap. 



Plants which have neither leaves nor 

 roots are of course unable either to draw 

 up a supply of crude sap or to elaborate 

 the juices required to sustain life. They 

 therefore resort to nefarious practices, and 

 live, like the feudal barons in the days of 

 King Stephen, by plundering their neigh- 

 bours. Of this sort are the Dodders 

 (Cuscuta\ the Broomrapes (Orobanche), the 

 Balanophorales, the Rafflesiales, and a 

 great many more of the plants so well 

 named parasites. We will say nothing of 

 the Mistletoe (Viscum album), which is, 

 comparatively speaking, a mild offender, 

 and, moreover, possesses true leaves (fig. 187). The germination of the 

 Dodder (fig. 189) is effected, like that of plants in general, in the earth, 

 and without requiring the presence of other plants. The embryo 

 which, unlike the embryos of most Flowering Plants, has no external 

 reserve of food material to feed upon is nourished, in its first develpment, 

 at the expense of the albuminous matter ivithin itself. The slender and 

 elementary root pushes its way into the earth, and the young, red, thread- 

 like stem rises above it. If it^finds no other living plant near it, it dies ; 



Photo by] [E. Step. 



FIG. 190. LARGE BROOMRAPE 



(Orobanche major). 



Parasitic chiefly on roots of Furze and Broom. 

 height of two feet. 

 N. AFRICA. 



Grows to 



EUROPE, 



