Nov., 1923] 
BAILEY-CAMBIUM AND DERIVATIVE TISSUES 
501 
less specialized dicotyledons, where the fluctuations in cell size are con¬ 
siderable, the normal curve of average length of the fusiform initials at 
successive ages is of the general type illustrated in text figure 1. There is a 
rapid increase in length for a period of years until a certain size is attained 
which then remains more or less constant during succeeding growth of the 
plant. Are these variations in cell size significant factors in the increase in 
girth of the lateral meristem during the earlier stages in the enlargement of 
a stem? Some typical measurements taken from Pinus Strobus L. are of 
interest in this connection. 
One-year-old stem 
Radius of woody cylinder. 2,000 microns 
Circumference of cambium. 12,566 microns 
Average length of fusiform initials. 870 microns 
Average tangential diameter of fusiform initials. 16 microns 
Number of fusiform initials in a cross section of stem. 724 microns 
Average tangential diameter of ray initials. 14 microns 
Number of ray initials in a cross section of stem. 70 microns 
60 -year-old stem 
Radius of woody cylinder. 200,000 microns 
Circumference of cambium. 1,256,640 microns 
Average length of fusiform initials. 4,000 microns 
Average tangential diameter of fusiform initials. 42 microns 
Average tangential diameter of ray initials. 17 microns 
The increase in width of the original 724 fusiform initials would produce, 
during the 59-year interval, an arc of 30,408 microns, and the increase in 
the diameter of the 70 ray initials, during the same interval, an arc of 1,190 
microns; or a total circumference of 31,598 microns as compared with the 
actual circumference of 1,256,640 microns. In other words, the enlargement 
of the cambial ring, during the 59-year interval, is due primarily to an in¬ 
crease in the number of initials; from 724 to 23,100 fusiform initials and 
from 70 to 8,796 ray initials. 
It is to be emphasized in this connection that such a multiplication of 
cambial initials— as seen in any given transverse plane or cross section of a 
stem —is not due necessarily to cell division. For, if the initials elongate 
and slide by one another, the number which intersect a given transverse 
plane will be continually augmented. However, if the increase in the 
number of fusiform initials in Pinus Strobus were due entirely to longi¬ 
tudinal sliding growth, the original initials, during the 59-year interval, 
would have to attain an average length of approximately 26,800 microns 
instead of 4,000 microns. The ray initials do not elongate to any consider¬ 
able extent. 
In exceptional cases, e.g., Sequoia, the fusiform initials may attain a 
maximum variability in length of 9,000 microns and in width of 60 microns, 
