ROOT AND STEM 109 
grow cuttings? Where roots are succulent—that is, 
when they have a reserve of food stored in them— 
cuttings of them will conversely produce stems. A 
classical instance of such interchangeability of func- 
tion is the young willow which Lindley bent down and 
buried the top till it rooted; the original roots were 
then dug up and raised into the air, when they pro- 
duced leafy branches, and the tree grew upside down 
henceforth. Underground stems, also, of which there 
is a great variety, take on many of the characters of 
roots, and from an examination of a small piece of one 
it is often difficult to tell whether we are dealing with 
a root ora stem. The point at which root joins stem 
is, in fact, in many instances, so far as function is 
concerned, fixed only so long as the level of the 
surface remains fixed: we can often alter it by 
“earthing up” or by stripping away the soil. In 
Tropical forests, where the air is moist, hot, and 
still, roots—or branches which serve only as roots— 
descend through the air from heights almost equalling 
those to which stems ascend; while, on the other hand, 
in hot, poorly aerated swamps, roots send up from 
the mud into the air stem-like structures (pneumato- 
phores) through which they may breathe, as in the 
case of the Swamp Cypress (J axodium distichum) of 
Florida. The primary differences between the two, 
in fact, do not prevent the one from taking on the 
general characters of the other, and from functioning 
as the other, when the environment changes. 
The stems of plants may be looked on from two 
points of view—as a framework devoted to the display 
of the leaves and flowers, and as pipe-lines connected 
with the nutrition of the plant, conveying raw 
