400 GEOGRAPHICAL BOTANY. 



ficient power the plants living beneath." This problem 

 may be expressed more definitely as follows. We have 

 to explain why the shadow of obscure deciduous forests 

 in the temperate zone are principally illuminated by 

 transmitted, and in the tropics by reflected light, and 

 why the Coniferous forests are poorer in these two lumi- 

 nous sources, and therefore so frequently deprived of 

 plants growing in the shade. We first think of the 

 Mimosa and forms of Palms, of the compound, and 

 therefore imperfectly shading forms of leaves, which 

 thus contribute powerfully to the light tone of the tropi- 

 cal forests. But trees possessing this character form a 

 part only, not the whole ; for those forms with simple 

 leaves, as the laurel- and Bombax-type, preponderate, in 

 variety of form or size of the leaf. And even the form of 

 the leaves of the Lauracese, which recurs in so many 

 tropical families, is wanting in that transparent texture 

 to which the light of the half-shaded parts of the northern 

 deciduous forests is owing. But Kittlitz has pointed out 

 another more universal character of the trees of tropical 

 forests, in the arrangement of the leaves, which appears 

 intended to complete the former. In climates where cold 

 or aridity cause the winter-sleep of woody plants, they 

 develope a very much larger number of small branches, 

 which usually form a more connected, although on the 

 whole poorer, stratum of leaves than in the tropics. 

 This, therefore, throws a deeper shadow upon the 

 ground, although it is more transparent ; not so deep, 

 however, as in the Coniferous forests, the crowded 

 leaves of which are opaque. On the other hand, it is 

 evident that the uninterrupted heat and moisture of 

 the equatorial climate also ensure a longer duration of 

 the first-formed branches, many of which, in the temperate 

 zone, fall off or remain undeveloped, and must therefore 

 produce fresh ramifications to allow of the necessary num- 

 ber of leaves being formed ; these first branches attracting 

 the currents of sap, continue to grow excentrically, and 

 hence leave between their uppermost tufts of leaves, i. e. 



