ANOMALOUS EXOGENOUS STEMS. 



49 



the stem assumes a peculiar lobed and sinuous aspect, and in some woody 

 climbing plants, pressure 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. 

 109). In Firs, the wood is occasionally produced in an oblique in 

 place of a perpendicular 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 

 parents. 



Fig. IOC. Horizontal section of the stem of Paullinia pinnata, one of the Sapindaceae of 

 Brazil, showing numerous secondary woody masses, surrounding a central one. Each of the 

 separate masses has pith, often excentric, with a medullary sheath, containing spiral vessels, 

 and a few medullary rays chiefly towards the circumference of the stem. 



Fig. 107. Horizontal section of the stem of Bignonia capreolata, showing the crucial division 

 of the woody layers. 



Fig. 108. Horizontal section of stem of Heteropterys anornala, one of the Brazilian Mal- 

 pighiacea?, showing an irregularly lobed surface. The dots indicate porous vessels. 



Fig. 109. Fragment of a stem of a climbing species of Banistcria (B. scandens) showing the 

 effects of compression^ 



E 



