522 



SIGNIFICANCE OF CAMBIUM 



Owing to the fact that the initials do not divide and elongate in 

 unison, there is usually a very considerable variabiKty in the length, 

 and pari passu in the volume, of adjacent elements. As shown in 

 Text-fig. 1, the average, maximum and minimum lengths of the cells 

 are considerably less in very young, slender, than in old, robust stems 

 and roots; but the values do not continue to increase throughout the 



B 



E 



Text-Fig. 3. Acute intersections of division membranes. A, from initial 

 dividing to form callus. B, C, and E, from initials dividing pseudotransversely. 

 D, from initial dividing unequally to form new ray initials. 



entire life of an individual. On the contrary, the curve of average 

 length at successive ages is of the general type illustrated in Text-fig. 

 2 (A). There is a rapid increase in length for a period of years 

 until a certain size is attained, which then remains constant during 

 succeeding growth.* A similar, though much less striking, increase 



^ The curve for any particular level or radius of a tree usually fluctuates about 

 this norm, owing to the effects of various environmental factors. 



