METAMORPHOSIS OF OEGANS OF PLANTS. 
95 
nation of the seed to the full growth of the plant, the formation 
of the flower, and the perfection of the new seed. We see in- 
stances of the abnormal process in cultivated plants, where an 
excess of nourishment causes a plethora, and organs which 
would otherwise have gone on to become stamens and pistils, re- 
main partially formed ; this may be seen in petals which appear 
to have assumed in part the appearance of stamens or pistils. 
It is not that usually the perfect stamen or pistil goes back to 
become a petal, but the natural progression is from the calyx 
to the petal, from that to the stamen, while the crowning of the 
work is the formation of the pistil ; an essential part of which 
is the germ, or envelope containing the new seed or future 
plant. Between the perfect stamens and outer row of petals 
m double flowers, as peonies, roses, tulips, &c., may be traced 
the gradual transformation of the petals to stamens ; next to 
perfect petals, appear those which are imperfectly formed, then 
a petal with a distorted limb on one side, and an imperfect an- 
ther or filament on the other. There is, in some cases, a retro- 
grade transformation of pistils into petals, as in double roses ; 
and in others of pistils into stamens. 
107. The axis of a plant is that part around which all the or- 
gans or parts center. The root is the descending axis^ the stem 
the ascending axis. On the germinating of a seed, the as- 
cending axis appears as a bud, or growing point.^ protected by 
rudimentary scales which gradually expand into leaves below, 
while new leaves are developing above. The axis is always 
terminated by a bud, and is thus elongated in one direction, or 
grows upward. During the growth of the stem its elongation 
is checked at intervals, by which narrow portions called nodes 
are rendered more firm than the spaces between them, which 
are called internodes. The nodes sometimes form entire rings 
round the stem; sometimes they are divided, appearing as 
scattered points on the circumference. From the nodes, under 
ordinary circumstances, all buds, and consequently all leaves 
and branches, originate. The manner in which branches come 
oif from the nodes causes the different forms of trees, as pyram- 
idal, spreading, or weeping; the angles formed by the stem 
being more or less acute or oblique. In the Lombardy poplar 
the branches are erect, forming acute angles with the upper 
part of the stem ; in the oak they are spreading, forming nearly 
a right angle ; in the weeping-willow they are pendent, being 
more flexible. The comparative length of the upper and un- 
der branches also gives rise to the difterence in the contour of 
trees, as may be seen in the conical form of some, and the um- 
brella-like form of others. 
AWrma process— Retrograde. — 107. Axis of the plant— Bwd— Nodes— Internodes— Branche*. 
