PARKINSONIA. 25 
be found in the wood. The wood parenchyma in the immediate vicinity 
of the ducts may contain chlorophyll (fig. 10). 
As to chlorophyll in the pith, it need only be said that it occurs sparingly 
in stems 1 cm. in diameter and is not present in the older and larger branches. 
The chlorophyll disappears from the stem in a very regular sequence. 
It leaves the epidermis first, then the pith, then the inner medullary rays; 
after this the wood parenchyma, then the medullary rays of the cortex and 
the median band, and finally, when cork is formed, the outer band. That 
is, with two exceptions, the chlorophyll disappears from the stem in a cen- 
trifugal direction. The exceptions were most marked in stem of P. forreyana 
8 mm. in diameter, in which practically all of the chlorophyll of the pith, 
as well as of the medullary rays of the wood, had been removed, but the 
deeply-placed wood parenchyma near the ducts still contained chlorophyll 
in considerable quantity. 
The leading departures from the chlorophyll conditions shared in common 
by the three species of Parkinsonia are as follows: P aculeata: Branches 
7 and 12 mm. in diameter had no chlorophyll in pith or in the inner part 
of the wood. P. microphylla: A variation due possibly to differences in 
water relations was observed in branches 1 cm. in diameter. One branch, 
taken from a tree which was apparently poorly supplied with water, had 
very little chlorophyll in the wood and none in the pith, while another 
branch of the same diameter, taken from a tree that had been irrigated at 
frequent intervals, had the maximum distribution of chlorophyll. P. zor- 
rveyana; As may be implied froma previous statement, this species appears 
not usually to have so much chlorophyll in its branches as the other ones, 
but an exception was noted in a stem 2.25 cm. in diameter, in which the 
chlorophyll was in the epidermis and extended into the stem for a distance 
of 6mm. This tree was growing ina particularly favorable location in 
the wash at the west base of Tumamoc Hill. 
The following measurements were made: 
5 Outer cortical band. | penetration 
Species. aren of chioro- 
Depth. Width. phyll. 
mm, & B mm. 
P, aculeata.......ecceeeeeeeee Fo | tease 960 0.6 
P. microphylla...... 3 83 83 Tg 
DO seievesssesssese- TOD |) cSseee. ||| eens 0.5 
DO sesesssesseuessrs t1.5 144 130 1.8 
DO 'sceescineccucgss 15 112 144 1.5 
DO i: csasecswrceess 32-5 160 234 1.6 
DOs iicascsvecessanncs 49 130 240 2 
DO tess nesiiersetiennen 80 160 TOO; |) aatous 
P. torreyana.........++ 8 64 TAG || seiecteas 
Onesstecacarensecae vesees 10 96 176 5 
D Owrseesesscoeviatsnees 12.5 96 160 | cesses 
DD Geiecenasiecoe eeeeeae’ 22.5 96 196 6 
DOuwrsececsceccenencerseeees 30 128 224 0.4 
