ANOMALOUS EXOGENOUS STEMS. 



G3 



considers them as connected witli the formation of leaves, and as 

 depending on a peculiar tendency 

 of the vascular bundles to be de- 

 veloped independently of each 

 other round several centres. 



In some Bignoniacese (fig. 

 125), the layers of wood are di- 

 ivided in a crucial manner into 

 four wedge-shaped portions by the 

 intervention of plates differing in 

 texture from the ordinary wood of 

 the plant, and probably formed by 

 introversion, or growing inwards 

 of the liber. In some Guayaquil 

 Bignonias, Gaudichaud perceived 

 first four of these plates, next 

 eight, then sixteen, and finally 

 thirty-two. In Aspidosperma 

 excelsum (Paddle- wood) of Guiana, 

 and in Heteropterys anomala (fig. 

 126), the stem assumes a peculiar 

 lobed and sinuous aspect ; and in 

 some woody climbing plants, pres- 

 sure causes the stems to become 

 flattened on the side next the tree 

 on which they are supported, while 

 from being twisted alternately in 

 different directions, they present a 

 remarkable zigzag form, having 

 the woody layers developed only 

 on one side (fig. 127). In Firs 

 the wood is occasionally produced 

 in an oblique in place of a per- 

 pendicular manner, thus injuring 

 the timber, and causing it to split 

 in an unusual way. The young 

 plants produced from the seed of 

 such twisted- wooded firs 

 are said to inherit the 

 peculiarity of their pa- 

 rents. Occasionally the 

 dicotyledonous stem, be- 

 comes swollen at certain 

 places, especially near the root, and thus exhibits a tuberous appear- 



Hg. 128. 



Fig. 128. Swollen stem of Irisli Tew (Taxus liaooata, va/r. striota). 



