ROUINSON : SlMNKS OI^ FoUQriF.RIA 



47 



3. t) 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 ca.st 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 



Fig. 4. Diagram of longitudinal section through petiole of Fouquieria splendens. 

 p, parenchyma ; s, sclerenchyma ; v, vascular tissue. 



Fk;. 5. Diagram of longitudinal section through petiole oi Fouquieria Mac- 



dougalii. 



Fig. 6. Diagram of transverse section through petiole of Fouquieria splendens near 



the apex of spine. 



Fig. 7. Diagram of transverse section through petiole of Fouquieria splendens, 



near base. 



Fig. 8. Diagram of transverse section through petiole of Fouquieria Macdougalii 



near base. 



Fig. 9. Diagram of transverse section through petiole of Fouquieria Macdout:^alii 

 near the apex of spine. 



in extent (Fig. 13, d). 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 Fouquieria 

 Macdougalii (Fig. 10, /') when they are young, but in F. splendens 

 they are less yielding. 



