PINUS. STEM. 141 



has been completed by the formation of an Interfasci- 

 cular cambium in the parenchyma between the 

 original bundles. 



Observe that the internal limit of the vascular ring 

 is sinuous. The convexities mark the position of the 

 primary bundles ; at the apex of these will be found 

 the Protoxylem. 



4. The Pith, consisting of parenchyma, having the 

 same characters as in the bud. No resin-passages. 



Put on a high power, and examine the Cambium. 

 Note 



i. That the cells are arranged with great regularity in 

 radial rows. 



ii. That their walls are thinner than those of the 

 surrounding tissues, and are composed of .cellulose (blue 

 with Schulze's solution). 



iii. That the tangential walls are thinner than the 

 radial. 



iv. That the cells have copious protoplasm, in which 

 a Nucleus may often be recognised. 



These facts point to a repeated division of cells by 

 tangential walls. 



Draw carefully, and compare several of the radial series of cells 

 of the cambium. They will be found to coincide with Sanio's 

 law of cambial division, which was first concluded from obser- 

 vations on Pinus sylvestris. 



Observe, here and there, radial rows of which the 

 cells are more elongated in a radial direction than the 

 rest. These may be traced outwards towards the cortex 

 and inwards towards the pith. They are the Medullary 

 rays. Some of them may be traced the whole way to 

 the cortex and to the pith (primary medullary rays) f 



