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standing excessive insolation in a tropical chimate. 1 This colouration is 

 enhanced by stiff, adpressed hairs, which densely clothe the entire plant 

 and may serve as a means of resistance or protection to the excessive heat 

 and intense illumination to which the plant is exposed. The hairiness, 

 according to the interpretation of M. Mer and the Eev. Gr. Henslow, may 

 have been formed, cceteris paribus, as compensation for the arrest of the 

 development of parenchymatous tissue produced by dryness as well as by 

 the barrenness of the soil. 



The next point to be noticed is the spiniscent character found in the 

 apex of the leaves of this plant. The hardness of the stem, the rigidity 

 of the branches, and the spiniscence of the leaves, as observed by the Rev. 

 G. Henslow, are " due to a want of water, which prevents the formation 

 of cellular tissue ; while this deficiency of parenchyma is associated with a 

 hardening of the flbro- vascular mechanical elements." 



It is quite natural that, in those arid districts, the soil would contain 

 a less quantity, or an excess of certain kinds, of nutritive substances required 

 by the plants in fertile lands. Now, the stem and branches of the African 

 specimens, are found to be covered with wool, cotton, feathers, dried leaves, 

 and organic dust, which either cling to the spiniscent leaves or adhere to 

 the stiff hairs. These organic matters being in a state of dryness and 

 decomposition, may be dissolved by occasional showers, the water flowing 

 down the stem and branches, and finally collecting about the roots, thus 

 furnish an additional supply of nutrition to the plant. 



It may be noted that the African plant grows not only in littoral 

 regions, but also, as in the case of my specimens, penetrates some miles 

 into the interior, where the soil is arid and desolate. 



Next we shall examine the Chinese plant, Salsola collina. The 

 specimen, collected on the coast of North China, displays wonderful similarity 

 in its habits even to minute details, except that in the Chinese specimen, 

 the entire plant is smooth, while the African specimens are covered with 

 stiff hairs; that in the former, the stem and branches are coloured with 

 green or reddish stripes ; and that, while the floral-leaves are spiniscent, 

 the cauline ones retain their normal form, being filiform or lineal, and are 

 between 5 and 30 mm. long. This dimorphism, formed by adaptation to 

 their environment, in the leaves of Salsola collina, is interesting: from an 

 ecological standpoint as representing modifications from normal leaves to 

 spiniscent ones, the latter form alone, however, is to be observed in Salsola 



1. Eev. G. Henslow: On the Origin of Plant Structures by Self- Adaptation to the 

 Environment, etc. (Journal of the Linnean Society, XXX, 1894, Xo. 208). 



