46 ROBINSON : SPINES OF FOUQUIERIA 
On the lower side of the petiole of the primary leaves, a woody 
thickening is developed (Fics. 11 and 12, w) which increases in 
firmness as the leaf matures. This arises from the cortex, which 
even in the bud is proliferated to form 
a thickened area on the outer side of the 
base of each leaf (Fie. 1, c). As the 
leaf emerges from the bud a conical 
portion of the cortex on the lower side 
of the petiole begins to lose its paren- 
chymatous character. The cells lengthen, 
their énds become pointed (Fic. 2, s) and 
their walls thicken; these changes are 
WG: 3. Scctién through tad. accompanied by a diminution in their 
a, young leaf; ¢, cortex, thick- lumina (Fic. 3, s). With phloroglucin 
ened to form spine; v, vascular and hydrochloric acid they take the 
tissue. 
violet color characteristic of sclerenchy- 
matous cells. The conversion of the parenchyma into scleren- 
chyma is incomplete in / sflendens, and a slender cone shaped 
mass of thin-walled cells extends 
about two thirds of the distance 
from the base toward the tip 
of the newly formed spine. This 
is illustrated by the diagrams of 8 
longitudinal and transverse sec- fg 2, Portion of longitudinal section 
tions shown in Fics. 4,6 and 7, through petiole. 4, cortex; ¢, separating 
yp. About the time when the /#yer; 5, sclerenchyma. 
leaf-blade is cast off, the parenchyma-core disintegrates and a hol- 
low spine remains. In Fouquieria — 
Macdougalii, on the other hand, — 
almost the entire mass of the cor _ 
tex on the outer (lower) side of 
peer Sete: pase intof 
SLI IE REEEING OA the petiole is transformed el 
ERLE steenchyma, making 2 si 
Gong: SeenON a 1 _ < 
5 4 
s 
Fic. 3. Portion of transverse section 
through petiole. 
accompanied by the differentiation 2 
of a separatory layer of thin-walled, elongated cells (Fics. 2 and 
