33* 



ZONES AND REGIONS 



[Pt. Ill, Sect. I 



substance, or a mixture of both, which is excreted by colleters, and is 

 regarded as protective in function. Groom has published further details 



in regard to this matter. 



More remarkable even than the structure 

 of foliage-buds is, in many cases, their 

 manner of opening. Treub has very justly 

 remarked : ' Trees shoot out their leaves.' 

 One of the most astonishing phenomena of 

 tropical vegetation is that in many trees 

 the young leaves, as in Theobroma Cacao 

 and Mangifera indica (Fig. 177), or quite 

 young shoots, as in Brownea hybrida 

 (Fig. 175), Amherstia nobilis (Fig. 176) 

 and other Caesalpiniaceae, after having 

 attained their full size, hang down limply 

 like tassels and are usually also devoid of 

 chlorophyll, so that, by their white or rosy 

 red colour, they contrast with the green 

 foliage. The vertical position in the 

 pendent shoots is solely due to the want of 

 turgescence ; in pendent leaves it is caused 

 by the active curvature of the pulvinus 

 as well. 



The pendent leaves are completely dif- 

 ferentiated only after having concluded 

 their superficial growth. Then it is that 

 chlorophyll appears in their hitherto colourless and small chromatophores, 

 whilst the originally homogeneous mesophyll differentiates into palisade- 



Fig. 173. 1. Tabernaemontana dicho- 

 toma ; terminal bud. 2. Clusia grandi- 

 flora (?) ; young shoot. After P. Groom. 



Fig. 1 74. Wormia Burbidgei. Leaf with bud concealed in the sheath. After P. Groom. 



tissue and spongy parenchyma, and thickens its delicate walls. These 

 processes are accompanied by a gradual assumption of a condition of 

 turgescence and of tension in the tissues. 



All authors who have described the above phenomenon have, possibly 



