tis 
ROBINSON : SPINES OF FOUQUIERIA 47 
3, ¢) in the cortex, between the sclerenchymatous tract and the 
fibrovascular tissue of the petiole. The sclerenchymatous tissue 
sustains only mechanical relations to the leaf, and the lamina may 
be held for extended periods after the completion of the separatory 
layer. When the vegetative season reaches its end by reason of 
drought or low temperature, the leaf-blade is cast off; and as its 
fall occurs simultaneously with its drying out, this desiccation may 
be taken as the direct cause of the splitting of the separatory 
layer above mentioned. The separation is identical with that 
which occurs in the fall of the leaves of many deciduous’ trees 
in the autumn in general procedure, but the author is not acquainted 
with any other instance in which the petiole is cut in a longitudinal 
plane making necessary a separatory layer two or three centimeters 
in tee itaenticeinet ral Et, siege ipa 
SS =e 
v 
v r 
. 8 
Fic. 4. Diagram of longitudinal section through petiole of Houguzerta splendens. 
P, parenchyma; s, sclerenchyma; v, vascular tissue. 
Fic. 5. Diagram of longitudinal section through petiole of /ouguieria Mac- 
dougaliz. 
Fic. 6. Diagram of transverse section through petiole of Fouguteria splendens near 
the ait of spine. 
G. 7. Diagram of transverse section through petiole of Fouguieria splendens, 
Fic. 8. Diagram of transverse section through petiole of Fouguieria Macdougalit 
near base. 
1G. 9. Diagram of transverse section through petiole of Fouguceria Macdougalit 
near the apex of spine. 
in extent (Fic. 1 3, @). Again, this unique method of excision re- 
sults in leaving an elongated pointed portion of the petiole 3 or 4 cm. 
in length attached to a mass of thickened epidermis and cork on 
the stem where it is retained rigidly for an indefinite period. The 
Spine and the contiguous portion of the outer tissues of the stem 
may easily be pulled from the underlying tissues in owguteria 
Macdougalii (Fic. 10, &) when they are young, but in F. splendens 
they are less yielding. 
