METAMORPHOSIS OF ORGANS OP PLANTS. 95 



nation of the seed to the full growth of the plant, the formation 

 of the flower, and the perfection of tlie 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 onto 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, wdiile the crowning of the 

 Avork is the formation of the ^^istil ; 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 7'etro- 

 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 pointy 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. Dm-ing the growth of the stem its elongation 

 is checked at intervals, by wdiich narrow portions called nodes 

 are rendered more firm than the spaces between them, w^hich 

 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 

 off from the nodes causes the difierent 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 x>oplar 

 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 difierence in the contour of 

 trees, as may be seen in the conical form of some, and the um- 

 brella-like form of others. 



Abnormal process— Retrograde.— 107. Axis of the plant— Bud— Nodes— Internodes— Branches. 



