334 FORM AND POSITION OF THE TRANSPIRING LEAVES AND BRANCHES. 



the whole. The Butcher's-brooms, chosen above as examples, belong to Southern 

 Europe, and occur in large quantities on the soil of dry woods, where everything is 

 wrapped in deep sleep during the height of summer. In the Antilles, and in the 

 prairies of the East Indies, are about twenty shrub -like species, belonging to 

 the genus Phyllanthus of the Spurge-family. New Zealand also possesses one of 

 these peculiar phyllocladous plants, belonging to the papilionaceous genus Car- 

 michelia. In the species of both these genera (see fig. 83) the flattened shoots are 

 exceedingly like lancet-shaped foliage-leaves, and the true leaves are transformed 

 into small pale scales. These tiny scales are situated on the margins of the 

 phylloclades, and from their axils arise stalks bearing the flowers and fruit. On 

 the Andes of South America occur the remarkable colletias, of which a species, 

 Colletia cruciata, is represented in fig. 83. The leaflets on these extraordinary 

 shrubs are diminutive, but not pale and scale-like; whilst the green phylloclades, 

 which play the part of the foliage-leaves, form very strong flattened organs, tapering 

 to a point, and placed opposite one another in pairs, so that each pair is always at 

 right angles to the couple next above or below. Yet another arrangement is seen 

 in Coccoloba platyclada (Polygonaceae), a native of the Salomon Islands, and in 

 Coceulus Balfou7'ii, growing in the island of Socotra. But it is impossible here to 

 enter into all these variations in detail ; it is enough to have brought forward 

 the most striking forms of phyllocladous plants which are represented in figs. 82 

 and 83. 



If in all these peculiar plants the branches are flattened and spread out, it 

 cannot indeed be asserted that the surface of their transpiring tissue has undergone 

 diminution, and thus far of course this strange development has nothing to do with 

 the restriction of transpiration. The arrangement by which this is brought about 

 must be sought for elsewhere. It consists in this: the leaf-like shoots are so 

 directed that their surfaces are vertical and not horizontal. Contrary to most flat 

 leaves, which turn their broad surfaces fully to the incident light, the flattened 

 shoots are placed vertically so that at mid-day they only cast a very narrow shadow, 

 and do not stop the sunbeams on their way to the soil. It is obvious, however, that 

 such a leaf-like structure placed vertically, as it were on edge, will exhale much less 

 than a foliage-leaf whose surface is opposed to the mid-day sunbeams. The work 

 carried on in the green cells, under the influence of light, is not hindered by this 

 position of the leaf-like organs. If the vertical green surfaces are not so well 

 illuminated by the sun's rays during the warmest part of the day, this is abundantly 

 compensated for by the fact that their broad surfaces are exposed to the light both 

 of the morning and evening sun. On the other hand, when the sun rises and sets, 

 the heat is not so powerful, and consequently there is no such rapid exhalation to 

 be feared as when the sun is in the zenith. To put the matter shortly, transpiration 

 alone — not illumination — is restricted by the vertical position of the green laminae, 

 and therefore this metamorphosis has rightly been considered a protective measure 

 against excessive transpiration. 



This arrangement is only found in plants of dry regions, where transpiration 



