-206 BOTANICAL GAZETTE [MARCH 
doubt these two processes overlap. For the sake of clearness in 
the subsequent discussion, however, growth in length will be con- 
sidered in the general sense of primary growth, growth in thickness 
as secondary growth. 
Awakening of secondary growth in aerial parts’ 
The awakening of secondary growth in aerial parts is first 
manifested in the cambium and the adjacent phloem tissue. It 
is evident in all cases several weeks before actual cell division begins. 
The cambial cells and last formed sieve tubes (6-10) open out 
radially, so that they attain several times their former diameter. 
Reference to the following table will show the changes which 
occurred between February 22, 1913 and March 29, 1913, in the 
width of cambium and last formed phloem. 
TABLE B 
GROWTH WITHOUT CELL DIVISION, TREE I 
Cutting ee nee mer ois |Per cent increase] — hel bine 
Pie 69.0K O1.5h 3°.6 013.3# 49.7 
Rois watson 89.1 110.6 24.0 182.9 105.3 
fo 8 Nee Soa ri 94.1 140.7 70.0 180.4 81.0 
EV oA aa 103.3 171.1 56.0 188.5 82.0 
In all cases, enlargement of the tissues in question occurred 
between the first two dates, and amounted from over a quarter to 
nearly three-quarters of their original size. The place of greatest 
enlargement was in cutting III, 17 feet from the ground. This 
does not correspond with the place of greatest ring thickening (table 
A) the previous year. Whether any significance can be attached 
to this discrepancy cannot be decided with certainty. It seems 
reasonable, however, to ascribe it to heightened temperature from 
the rise of soil water in the xylem.’ It would be natural to assume 
7 No ob tions have been made on lary growth in the leaves. MEISSNER 
(21) has observed a marked increase in the number of phloem elements and a very 
slight increase in the xylem elements in a number of species of Pinus. 
8 Ropr. Haptic (11, p. 262) made note of the temperature of soil water as 4 
factor potent in forwarding grow 
