MEANS OF ACCELERATING TRANSPIRATION. 287 



numerous other plants of the flora of Central Europe, which are sometimes to be 

 found in damp, shady woods, sometimes in sunny fields; but the above examples 

 will suffice to demonstrate the fact that in shady places and damp air, in spite of 

 the smaller amount of heat, and even when the humidity of the soil is less, the 

 leaves will, notwithstanding, have a greater size than in sunny places where they 

 are surrounded by a drier air. 



An apparent exception is to be found only when these plants are situated above 

 the tree-line in Alpine regions. On the sunny slopes of Monte Baldo, in Venetia, far 

 above the wood-line, Corydalis fabacea grows with the same luxuriance as in the 

 shady forests of the lower hilly regions; and on one place on the Solstein chain, in 

 the Tyrol, at a height of 1800 metres above the sea, dog's mercury and Galeobdolon 

 luteum, species of valerian, spurge-laurel, and ferns can be seen rising above the 

 boulders with leaves as large as those growing in the shade of the woods below. 

 But this exception, as stated, is only an apparent one. Where these plants flounsn 

 on Alpine heights flooded with light, the air is just as damp as in the depth of the 

 woods 1000 metres lower in the valley. For weeks the mist sways like drapery 

 around the heights, and the air, consequently, is certainly not drier than in the woods 

 down in the valley. Indeed, the fact that plants, which one is accustomed to see 

 inhabiting the shady woods in the depth of the valley, grow in Alpine regions on 

 unshaded places with leaves of the same size and shape as before, is a proof that 

 the large size of their leaves in the dark woods of these lower places is not due to 

 the absence of light, but to the very moist condition of the air which prevails there. 

 Plants, whether in the shade of the forests, or on the illuminated heights of the 

 mountains, endeavour to compensate for the detrimental influence of the greater 

 humidity of the air by the formation of an extensive transpiring surface. 



So far the increase of leaf surface may be considered absolutely as a means of 

 helping transpiration. This method of increasing transpiration comes into action 

 in the tropics in a much more striking way than even in the temperate zones. 

 Especially in the most characteristic plant-structures of the tropics may it be 

 observed how intimately the size of the leaves corresponds to the conditions of 

 moisture of the air, and how it is that palms develop the largest leaves just in those 

 districts where, in consequence of the air being saturated with aqueous vapour, 

 plants can only transpire with difficulty. In the dampest parts of Ceylon grows the 

 gigantic Corypha umbraculifera. A copy of a drawing of this tree, sketched on 

 the spot by Ransonnet, is given in fig. 63. It towers above the tops of all other 

 plants, and its leaf-blades are from 7 to 8 metres long, and 5 to 6 metres broad. 

 In similar situations in Brazil the palm Raphia tcedigera spreads out its fronds like 

 gigantic feathers. The petiole of this leaf alone is 4 to 5 metres long, and the green 

 feather-like blade is from 19 to 22 metres long and 12 metres broad — the greatest 

 extent which has hitherto been observed in any leaf. Other palms besides these 

 giants, whose fronds wave all the year round in a damp atmosphere, are but 

 little inferior to them. Under one leaf of the Talipot ten persons can easily 

 find room and shelter, and if the pinnate leaves of the Sago-palm be imagined 



