654 CONSERVATIVE ORGANS. [LECT. XI. 



and foliar (foliares), when they are a continuation 

 of the midrib of a simple leaf, as that of superb 

 Gloriosa, G. superba. The petiolar tendril is 

 sometimes distinguished by the number of leaf- 

 lets which grow under it; thence we find in sys- 

 tematic authors the terms Cirrhi diphylli, tetra- 

 phylli, and polyphylli. The flower-stalks even of 

 some plants, as those of smooth-leaved Heart- 

 seed, Cardiospermum Halicacabum, bear tendrils. 

 Tendrils closely resemble petioles in their struc- 

 ture ; but not so intimately as to lead us to adopt 

 the opinion of Willdenow, that they are merely 

 petioles, which not having exhausted their sap in 

 forming the leafy expansion, become too feeble to 

 keep their straight direction, and have thence ac- 

 quired their twisted shape*. If we examine a 

 transverse slice of a tendril of Bryony, under the 

 microscope, and compare it with a slice of the 

 petiole which rises at its side, we shall find that 

 although they agree in some particulars, yet, they 

 differ in others. The cortex of both closely re- 

 sembles that of the stem (see p. 415) ; and the 

 internal structure in both, also, consists of fas- 

 ciculi of spiral and proper vessels embedded in a 

 cellular parenchyma. But the number of these 

 fascicles in the petiole is always nine, and in the 

 tendril four or five only: in the former, also, the 



* Principles of Botany, 271. 



